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Table of Contents

IP Commands

IP Commands

The Internet Protocol (IP) is a packet-based protocol used to exchange data over computer networks. IP handles addressing, fragmentation, reassembly, and protocol demultiplexing. It is the foundation on which all other Internet protocols, collectively referred to as the Internet Protocol suite, are built. IP is a network-layer protocol that contains addressing information and some control information that allows data packets to be routed.

The Transmission Control Protocol (TCP) is built upon the IP layer. TCP is a connection-oriented protocol that specifies the format of data and acknowledgments used in the transfer of data. TCP also specifies the procedures that the computers use to ensure that the data arrives correctly. TCP allows multiple applications on a system to communicate concurrently because it handles all demultiplexing of the incoming traffic among the application programs.

Use the commands in this chapter to configure and monitor IP networks. For IP protocol configuration information and examples, refer to the "Configuring IP" chapter of the Router Products Configuration Guide.

access-class

To restrict incoming and outgoing connections between a particular virtual terminal line (into a Cisco device) and the addresses in an access list, use the access-class line configuration command. To remove access restrictions, use the no form of this command.

access-class access-list-number {in | out}
no access-class access-list-number {in | out}

Syntax Description

access-list-number

Number of an access list. This is a decimal number from 1 through 99.

in

Restricts incoming connections between a particular Cisco device and the addresses in the access list.

out

Restricts outgoing connections between a particular Cisco device and the addresses in the access list.

Default

No access lists are defined.

Command Mode

Line configuration

Usage Guidelines

Remember to set identical restrictions on all the virtual terminal lines because a user can connect to any of them.

To display the access lists for a particular terminal line, use the show line EXEC command and specify the line number.

Examples

The following example defines an access list that permits only hosts on network 192.89.55.0 to connect to the virtual terminal ports on the router:

access-list 12 permit 192.89.55.0 0.0.0.255 line 1 5 access-class 12 in

The following example defines an access list that denies connections to networks other than network 36.0.0.0 on terminal lines 1 through 5:

access-list 10 permit 36.0.0.0 0.255.255.255 line 1 5 access-class 10 out
Related Command

A dagger (†) indicates that the command is documented in another chapter.

show line

access-list (standard)

To define a standard IP access list, use the standard version of the access-list global configuration command. To remove a standard access lists, use the no form of this command.

access-list access-list-number {deny | permit} source [source-wildcard]
no access-list
access-list-number

Caution Enhancements to this command are backward compatible; migrating from existing releases to Release 10.3 will convert your access lists automatically. However, releases prior to Release 10.3 are not upwardly compatible with these enhancements. Therefore, if you save an access list with these images and then use software prior to Release 10.3, the resulting access list will not be interpreted correctly. This could cause you severe security problems. Save your old configuration file before booting these images.
Syntax Description

access-list-number

Number of an access list. This is a decimal number from 1 through 99.

deny

Denies access if the conditions are matched.

permit

Permits access if the conditions are matched.

source

Number of the network or host from which the packet is being sent. There are two alternative ways to specify the source:

  • Use a 32-bit quantity in four-part dotted-decimal format.

  • Use the keyword any as an abbreviation for a source and source-wildcard of 0.0.0.0 255.255.255.255.

source-wildcard

(Optional) Wildcard bits to be applied to the source. There are two alternative ways to specify the source wildcard:

  • Use a 32-bit quantity in four-part dotted-decimal format. Place ones in the bit positions you want to ignore.

  • Use the keyword any as an abbreviation for a source and source-wildcard of 0.0.0.0 255.255.255.255.

Default

The access list defaults to an implicit deny statement for everything. The access list is always terminated by an implicit deny statement for everything.

Command Mode

Global configuration

Usage Guidelines

Plan your access conditions carefully and be aware of the implicit deny statement at the end of the access list.

You can use access lists to control the transmission of packets on an interface, control virtual terminal line access, and restrict the contents of routing updates.

Use the show access-lists EXEC command to display the contents of all access lists.

Use the show ip access-list EXEC command to display the contents of one access list.

Examples

The following example of a standard access list allows access for only those hosts on the three specified networks. The wildcard bits apply to the host portions of the network addresses. Any host with a source address that does not match the access list statements will be rejected.

access-list 1 permit 192.5.34.0 0.0.0.255 access-list 1 permit 128.88.0.0 0.0.255.255 access-list 1 permit 36.0.0.0 0.255.255.255 ! (Note: all other access implicitly denied)

To specify a large number of individual addresses more easily, you can omit the wildcard if it is all zeros. Thus, the following two configuration commands are identical in effect:

access-list 2 permit 36.48.0.3 access-list 2 permit 36.48.0.3 0.0.0.0
Related Commands

access-class
access-list (extended)
distribute-list in
distribute-list out
ip access-group
priority-list
queue-list
show access-lists
show ip access-list

access-list (extended)

To define an extended IP access list, use the extended version of the access-list global configuration command. To remove the access lists, use the no form of this command.

access-list access-list-number {deny | permit} protocol source source-wildcard destination
destination-wildcard
[precedence precedence] [tos tos]
no access-list access-list-number


For ICMP, you can also use the following syntax:

access-list access-list-number {deny | permit} icmp source source-wildcard destination
destination-wildcard [icmp-type [icmp-code] | icmp-message]
[precedence precedence]
[tos tos]

For IGMP, you can also use the following syntax:

access-list access-list-number {deny | permit} igmp source source-wildcard destination
destination-wildcard [igmp-type]
[precedence precedence] [tos tos]

For TCP, you can also use the following syntax:

access-list access-list-number {deny | permit} tcp source source-wildcard
[operator port [port]] destination destination-wildcard
[operator port [port]] [
established] [precedence precedence] [tos tos]

For UDP, you can also use the following syntax:

access-list access-list-number {deny | permit} udp source source-wildcard
[operator port [port]] destination destination-wildcard
[operator port [port]]
[precedence precedence] [tos tos]

Caution Enhancements to this command are backward compatible; migrating from existing releases to Release 10.3 will convert your access lists automatically. However, releases prior to Release 10.3 are not upwardly compatible with these enhancements. Therefore, if you save an access list with these images and then use software prior to Release 10.3, the resulting access list will not be interpreted correctly. This could cause you severe security problems. Save your old configuration file before booting these images.
Syntax Description

access-list-number

Number of an access list. This is a decimal number from 100 through 199.

deny

Denies access if the conditions are matched.

permit

Permits access if the conditions are matched.

protocol

Name or number of an IP protocol. It can be one of the keywords eigrp, gre, icmp, igmp, igrp, ip, ipinip, nos, ospf, tcp, or udp, or an integer in the range 0 through 255 representing an IP protocol number. To match any Internet protocol, including ICMP, TCP, and UDP, use the keyword ip. Some protocols allow further qualifiers described below.

source

Number of the network or host from which the packet is being sent. There are three alternative ways to specify the source:

  • Use a 32-bit quantity in four-part dotted-decimal format.

  • Use the keyword any as an abbreviation for a source and source-wildcard of 0.0.0.0 255.255.255.255.

  • Use host source as an abbreviation for a source and source-wildcard of source 0.0.0.0.

source-wildcard

Wildcard bits to be applied to source. There are three alternative ways to specify the source wildcard:

  • Use a 32-bit quantity in four-part dotted-decimal format. Place ones in the bit positions you want to ignore.

  • Use the keyword any as an abbreviation for a source and source-wildcard of 0.0.0.0 255.255.255.255.

  • Use host source as an abbreviation for a source and source-wildcard of source 0.0.0.0.

destination

Number of the network or host to which the packet is being sent. There are three alternative ways to specify the destination:

  • Use a 32-bit quantity in four-part dotted-decimal format.

  • Use the keyword any as an abbreviation for the destination and destination-wildcard of 0.0.0.0 255.255.255.255.

  • Use host destination as an abbreviation for a destination and destination-wildcard of destination 0.0.0.0.

destination-wildcard

Wildcard bits to be applied to the destination. There are three alternative ways to specify the destination wildcard:

  • Use a 32-bit quantity in four-part dotted-decimal format. Place ones in the bit positions you want to ignore.

  • Use the keyword any as an abbreviation for a destination and destination-wildcard of 0.0.0.0 255.255.255.255.

  • Use host destination as an abbreviation for a destination and destination-wildcard of destination 0.0.0.0.

precedence precedence

(Optional) Packets can be filtered by precedence level, as specified by a number from 0 to 7 or by name as listed in the section "Usage Guidelines."

tos tos

(Optional) Packets can be filtered by type of service level, as specified by a number from 0 to 15 or by name as listed in the section "Usage Guidelines."

icmp-type

(Optional) ICMP packets can be filtered by ICMP message type. The type is a number from 0 to 255.

icmp-code

(Optional) ICMP packets which are filtered by ICMP message type can also be filtered by the ICMP message code. The code is a number from 0 to 255.

icmp-message

(Optional) ICMP packets can be filtered by an ICMP message type name or ICMP message type and code name. The possible names are found in the section "Usage Guidelines."

igmp-type

(Optional) IGMP packets can be filtered by IGMP message type or message name. A message type is a number from 0 to 15. IGMP message names are listed in the section "Usage Guidelines."

operator

(Optional) Compares source or destination ports. Possible operands include lt (less than), gt (greater than), eq (equal), neq (not equal), and range (inclusive range).

If the operator is positioned after the source and source-wildcard, it must match the source port.

If the operator is positioned after the destination and destination-wildcard, it must match the destination port.

The range operator requires two port numbers. All other operators require one port number.

port

(Optional) The decimal number or name of a TCP or UDP port. A port number is a number from 0 to 65535. TCP port names are listed in the section "Usage Guidelines." TCP port names can only be used when filtering TCP. UDP port names are listed in the section "Usage Guidelines." UDP port names can only be used when filtering UDP.

TCP port names can only be used when filtering TCP. UDP port names can only be used when filtering UDP.

established

(Optional) For the TCP protocol only: Indicates an established connection. A match occurs if the TCP datagram has the ACK or RST bits set. The nonmatching case is that of the initial TCP datagram to form a connection.

Default

An extended access list defaults to a list that denies everything. An extended access list is terminated by an implicit deny statement.

Command Mode

Global configuration

Usage Guidelines

You can use access lists to control the transmission of packets on an interface, control virtual terminal line access, and restrict contents of routing updates. The router stops checking the extended access list after a match occurs.

Fragmented IP packets, other than the initial fragment, are immediately accepted by any extended IP access list. Extended access lists used to control virtual terminal line access or restrict contents of routing updates must not match against the TCP source port, the type of service value, or the packet's precedence.


Note After an access list is created initially, any subsequent additions (possibly entered from the terminal) are placed at the end of the list. In other words, you cannot selectively add or remove access list command lines from a specific access list.

The following is a list of precedence names:

The following is a list of type of service (tos) names:

The following is a list of ICMP message type names and ICMP message type and code names:

The following is a list of IGMP message names:

The following is a list of TCP port names that can be used instead of port numbers. Refer to the current Assigned Numbers RFC to find a reference to these protocols. Port numbers corresponding to these protocols can also be found by typing a ? in the place of a port number.

The following is a list of UDP port names that can be used instead of port numbers. Refer to the current Assigned Numbers RFC to find a reference to these protocols. Port numbers corresponding to these protocols can also be found by typing a ? in the place of a port number.

Examples

In the following example, serial interface 0 is part of a Class B network with the address 128.88.0.0, and the mail host's address is 128.88.1.2. The keyword established is used only for the TCP protocol to indicate an established connection. A match occurs if the TCP datagram has the ACK or RST bits set, which indicate that the packet belongs to an existing connection.

access-list 102 permit tcp 0.0.0.0 255.255.255.255 128.88.0.0 0.0.255.255 established access-list 102 permit tcp 0.0.0.0 255.255.255.255 128.88.1.2 0.0.0.0 eq 25 interface serial 0 ip access-group 102 in

The following example also permit DNS packets and ICMP echo and echo reply packets:

access-list 102 permit tcp any 128.88.0.0 0.0.255.255 established access-list 102 permit tcp any host 128.88.1.2 eq smtp access-list 102 permit tcp any any eq domain access-list 102 permit udp any any eq domain access-list 102 permit icmp any any echo access-list 102 permit icmp any any echo-reply
Related Commands

access-class
access-list (standard)
distribute-list in
distribute-list out
ip access-group
priority-list
queue-list
show access-lists
show ip access-list

arp (global)

To add a permanent entry in the ARP cache, use the arp global configuration command. To remove an entry from the ARP cache, use the no form of this command.

arp ip-address hardware-address type [alias]
no arp ip-address hardware-address type [alias]

Syntax Description

ip-address

IP address in four-part dotted-decimal format corresponding to the local data link address.

hardware-address

Local data link address (a 48-bit address).

type

Encapsulation description. For Ethernet interfaces, this is typically the arpa keyword. For FDDI and Token Ring interfaces, this is always snap.

alias

(Optional) Indicates that the router should respond to ARP requests as if it were the owner of the specified address.

Default

No entries are permanently installed in the ARP cache.

Command Mode

Global configuration

Usage Guidelines

The router uses ARP cache entries to translate 32-bit Internet Protocol addresses into 48-bit hardware addresses.

Because most hosts support dynamic resolution, you generally do not need to specify static ARP cache entries.

To remove all nonstatic entries from the ARP cache, use the clear arp-cache privileged EXEC command.

Example

The following is an example of a static ARP entry for a typical Ethernet host:

arp 192.31.7.19 0800.0900.1834 arpa
Related Command

clear arp-cache

arp (interface)

To control the interface-specific handling of IP address resolution into 48-bit Ethernet, FDDI, and Token Ring hardware addresses, use the arp interface configuration command. To disable an encapsulation type, use the no form of this command.

arp {arpa | probe | snap}
no arp {arpa | probe | snap}


Syntax Description

arpa

Standard Ethernet-style ARP (RFC 826).

probe

HP Probe protocol for IEEE-802.3 networks.

snap

ARP packets conforming to RFC 1042.

Default

Standard Ethernet-style ARP

Command Mode

Interface configuration

Usage Guidelines

Unlike most commands that take multiple arguments, arguments to the arp command are not mutually exclusive. Each command enables or disables a specific type of ARP. For example, if you enter the arp arpa command followed by the arp probe command, the router would send three (two for probe and one for arpa) packets each time it needed to discover a MAC address.

The arp probe command allows the router to use the Probe protocol (in addition to ARP) whenever it attempts to resolve an IEEE-802.3 or Ethernet local data link address. The subset of Probe that performs address resolution is called Virtual Address Request and Reply. Using Probe, the router can communicate transparently with Hewlett-Packard IEEE-802.3 hosts that use this type of data encapsulation.


Note Cisco's support for HP Probe proxy support changed as of Software Release 8.3(2) and subsequent software releases. The no arp probe command is now the default. All interfaces that will use Probe must now be explicitly configured for arp probe.

The show interfaces EXEC command displays the type of ARP being used on a particular interface. To remove all nonstatic entries from the ARP cache, use the clear arp-cache privileged EXEC command.

Example

The following example enables probe services:

interface ethernet 0 arp probe
Related Commands

clear arp-cache
show interfaces

arp timeout

To configure how long an entry remains in the ARP cache, use the arp timeout interface configuration command. To restore the default value, use the no form of this command.

arp timeout seconds
no arp timeout seconds

Syntax Description

seconds

Time, in seconds, that an entry remains in the ARP cache. A value of zero means that entries are never cleared from the cache.

Default

14400 seconds (4 hours)

Command Mode

Interface configuration

Usage Guidelines

This command is ignored when issued on interfaces that do not use ARP. The show interfaces EXEC command displays the ARP timeout value. The value follows the "Entry Timeout:" heading, as seen in this sample show interfaces display:

ARP type: ARPA, PROBE, Entry Timeout: 14400 sec
Example

The following example illustrates how to set the ARP timeout to 12000 seconds to allow entries to time out more quickly than the default:

interface ethernet 0 arp timeout 12000
Related Command

show interfaces

clear arp-cache

To delete all dynamic entries from the ARP cache, to clear the fast-switching cache, and to clear the IP route cache, use the clear arp-cache EXEC command.

clear arp-cache

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Example

The following example removes all dynamic entries from the ARP cache and clears the fast-switching cache:

clear arp-cache
Related Commands

arp (global)
arp (interface)

clear host

To delete entries from the host-name-and-address cache, use the clear host EXEC command.

clear host {name | *}

Syntax Description

name

Particular host entry to remove.

*

Removes all entries.

Command Mode

EXEC

Usage Guidelines

The host name entries will not be removed from NVRAM, but will be cleared in running memory.

Example

The following example clears all entries from the host name-and-address cache:

clear host *
Related Commands

show hosts
ip host

clear ip accounting

To clear the active or checkpointed database when IP accounting is enabled, use the clear ip accounting EXEC command.

clear ip accounting [checkpoint]

Syntax Description

checkpoint

(Optional) Clears the checkpointed database.

Command Mode

EXEC

Usage Guidelines

You can also clear the checkpointed database by issuing the clear ip accounting command twice in succession.

Example

The following example clears the active database when IP accounting is enabled:

clear ip accounting
Related Commands

ip accounting
ip accounting-list
ip accounting-threshold
ip accounting-transits
show ip accounting

clear ip nhrp

To clear all dynamic entries from the Next Hop Resolution Protocol (NHRP) cache, use the clear ip nhrp EXEC command.

clear ip nhrp

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Usage Guidelines

This command does not clear any static (configured) IP-to-NBMA address mappings from the NHRP cache.

Example

In the following example, all dynamic entries are cleared from the NHRP cache for the interface:

clear ip nhrp
Related Command

show ip nhrp

clear ip route

To delete routes from the IP routing table, use the clear ip route EXEC command.

clear ip route {network [mask] | *}

Syntax Description

network

Network or subnet address to remove.

mask

(Optional) Subnet address to remove.

*

Removes all routing table entries.

Default

All entries are removed.

Command Mode

EXEC

Example

The following example removes a route to network 132.5.0.0 from the IP routing table:

clear ip route 132.5.0.0

clear ip sse

To have the route processor recompute the SSE program for IP on the Cisco 7000 series, use the clear ip ssel EXEC command.

clear ip sse

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Privileged EXEC

Usage Guidelines

The silicon switching engine (SSE) is on the Silicon Switch Processor (SSP) board in the Cisco 7000.

This command also updates the SSE cache for IP.

Example

The following example causes the route processor to recompute the program for IP:

clear ip sse

clear sse

To reinitialize the route processor on the Cisco 7000 series, use the clear sse EXEC command.

clear sse

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

EXEC

Usage Guidelines

The silicon switching engine (SSE) is on the Silicon Switch Processor (SSP) board in the
Cisco 7000.

Example

The following example causes the route processor to be reinitialized:

clear sse

dnsix-dmdp retries

To set the retransmit count used by the DNSIX Message Delivery Protocol (DMDP), use the dnsix-dmdp retries global configuration command. To restore the default numbe of retries, use the no form of this command.

dnsix-dmdp retries count
no dnsix-dmdp retries count

Syntax Description

count

Number of times DMDP will retransmit a message. It can be a decimal integer from 0 through 200. The default is 4 retries, or until acknowledged.

Default

Retransmits messages up to 4 times, or until acknowledged

Command Mode

Global configuration

Example

The following example sets the number of times DMDP will attempt to retransmit a message to 150:

dnsix-dmdp retries 150
Related Commands

dnsix-nat authorized-redirection
dnsix-nat primary
dnsix-nat secondary
dnsix-nat source
dnsix-nat transmit-count

dnsix-nat authorized-redirection

To specify the address of a collection center that is authorized to change the primary and secondary addresses of the host to receive audit messages, use the dnsix-nat authorized-redirection global configuration command. To delete an address, use the no form of this command.

dnsix-nat authorized-redirection ip-address
no dnsix-nat authorized-redirection ip-address

Syntax Description

ip-address

IP address of the host from which redirection requests are permitted.

Default

An empty list of addresses

Command Mode

Global configuration

Usage Guidelines

Use multiple dnsix-nat authorized-redirection commands to specify a set of hosts that are authorized to change the destination for audit messages. Redirection requests are checked against the configured list, and if the address is not authorized the request is rejected and an audit message is generated. If no address is specified, no redirection messages are accepted.

Example

The following example specifies that the address of the collection center that is authorized to change the primary and secondary addresses is 193.1.1.1.

dnsix-nat authorization-redirection 193.1.1.1.

dnsix-nat primary

To specify the IP address of the host to which DNSIX audit messages are sent, use the dnsix-nat primary global configuration command. To delete an entry, use the no form of this command.

dnsix-nat primary ip-address
no dnsix-nat primary ip-address

Syntax Description

ip-address

IP address for the primary collection center.

Default

Messages are not sent.

Command Mode

Global configuration

Usage Guidelines

An IP address must be configured before audit messages can be sent.

Example

The following example configures an IP address as the address of the host to which DNSIX audit messages are sent:

dnsix-nat primary 194.1.1.1

dnsix-nat secondary

To specify an alternate IP address for the host to which DNSIX audit messages are sent, use the dnsix-nat secondary global configuration command. To delete an entry, use the no form of this command.

dnsix-nat secondary ip-address
no dnsix-nat secondary ip-address

Syntax Description

ip-address

IP address for the secondary collection center.

Default

No alternate IP address is known.

Command Mode

Global configuration

Usage Guidelines

When the primary collection center is unreachable, audit messages are sent to the secondary collection center instead.

Example

The following example configures an IP address as the address of an alternate host to which DNSIX audit messages are sent:

dnsix-nat secondary 193.1.1.1

dnsix-nat source

To start the audit-writing module and to define audit trail source address, use the dnsix-nat source global configuration command. To disable the DNSIX audit trail writing module, use the no form of this command.

dnsix-nat source ip-address
no dnsix-nat source ip-address

Syntax Description

ip-address

Source IP address for DNSIX audit messages.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

You must issue the dnsix-nat source command before any of the other dnsix-nat commands. The configured IP address is used as the source IP address for DMDP protocol packets sent to any of the collection centers.

Example

The following example enables the audit trail writing module, and specifies that the source IP address for any generated audit messages should be the same as the primary IP address of interface Ethernet 0.

dnsix-nat source 128.105.2.5
interface ethernet 0
ip address 128.105.2.5 255.255.255.0

dnsix-nat transmit-count

To have the audit writing module collect multiple audit messages in the buffer before sending the messages to a collection center, use the dnsix-nat transmit-count global configuration command. To revert to the default audit message count, use the no form of this command.

dnsix-nat transmit-count count
no dnsix-nat transmit-count count

Syntax Description

count

Number of audit messages to buffer before transmitting to the server. Integer from 1 through 200.

Default

One message is sent at a time.

Command Mode

Global configuration

Usage Guidelines

An audit message is sent as soon as the message is generated by the IP packet-processing code. The audit writing module can, instead, buffer up to several audit messages before transmitting to a collection center.

Example

The following example configures the system to buffer five audit messages before transmitting them to a collection center:

dnsix-nat transmit-count 5

ip access-group

To control access to an interface, use the ip access-group interface configuration command. To remove the specified access group, use the no form of this command.

ip access-group access-list-number {in | out}
no ip access-group access-list-number {in | out}

Syntax Description

access-list-number

Number of an access lists. This is a decimal number from 1 through 199.

in

Filters on inbound packets.

out

Filters on outbound packets.

Default

Entering a keyword is strongly recommended, but if a keyword is not specified, out is the default.

Command Mode

Interface configuration

Usage Guidelines

For inbound access lists, after receiving a packet, the router checks the source address of the packet against the access list. If the access list permits the address, the router continues to process the packet. If the access list rejects the address, the router discards the packet and returns an ICMP Host Unreachable message.

For outbound access lists, after receiving and routing a packet to a controlled interface, the router checks the source address of the packet against the access list. If the access list permits the address, the router transmits the packet. If the access list rejects the address, the router discards the packet and returns an ICMP Host Unreachable message.

Access lists are applied on either outbound or inbound interfaces.

If the specified access list does not exist, all packets are passed.

When you enable outbound access lists, you automatically disable autonomous switching for that interface.When you enable input access lists on any cBus or CxBus interface, you automatically disable autonomous switching for all interfaces (with one exception; an SSE configured with simple access lists can still switch packets, on output only).

Example

The following example applies list 101 on packets outbound from Ethernet 0:

interface ethernet 0 ip access-group 101 out
Related Commands

access-list (extended)
show access-lists

ip accounting

To enable IP accounting on an interface, use the ip accounting interface configuration command. To disable IP accounting, use the no form of this command.

ip accounting [access-violations]
no ip accounting [access-violations]

Syntax Description

access-violations

(Optional) Enables IP accounting with the ability to identify IP traffic that fails IP access lists.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

IP accounting records the number of bytes (IP header and data) and packets switched through the system on a source and destination IP address basis. Only transit IP traffic is measured and only on an outbound basis; traffic generated by the router or terminating in the router is not included in the accounting statistics.

If you specify the access-violations keyword, this command provides information identifying IP traffic that fails IP access lists. Identifying IP source addresses that violate IP access lists alerts you to possible attempts to breach security. The data might also indicate that you should verify IP access list configurations.

Statistics are accurate even if IP fast switching or IP access lists are being used on the interface.

IP accounting disables autonomous switching and SSE switching on the interface.

Example

The following example enables IP accounting on Ethernet interface 0:

interface ethernet 0 ip accounting
Related Commands

clear ip accounting
ip accounting-list
ip accounting-threshold
ip accounting-transits
show ip accounting

ip accounting-list

To define filters to control the hosts for which IP accounting information is kept, use the ip accounting-list global configuration command. To remove a filter definition, use the no form of this command.

ip accounting-list ip-address wildcard
no ip accounting-list ip-address wildcard

Syntax Description

ip-address

IP address in dotted-decimal format.

wildcard

Wildcard bits to be applied to ip-address.

Default

No filters are defined.

Command Mode

Global configuration

Usage Guidelines

The source and destination address of each IP datagram is logically ANDed with ones-complement of the wildcard and compared with the ip-address. If there is a match, the information about the IP datagram will be entered into the accounting database. If there is no match, the IP datagram is considered a transit datagram and will be counted according to the setting of the ip accounting-transits global configuration command.

Example

The following example adds all hosts with IP addresses beginning with 192.31 to the list of hosts for which accounting information will be kept:

ip accounting-list 192.31.0.0 0.0.0.255
Related Commands

clear ip accounting
ip accounting
ip accounting-threshold
ip accounting-transits
show ip accounting

ip accounting-threshold

To set the maximum number of accounting entries to be created, use the ip accounting-threshold global configuration command. To restore the default number of entries, use the no form of this command.

ip accounting-threshold threshold
no ip accounting-threshold threshold

Syntax Description

threshold

Maximum number of entries (source and destination address pairs) that the router accumulates.

Default

512 entries

Command Mode

Global configuration

Usage Guidelines

The accounting threshold defines the maximum number of entries (source and destination address pairs) that the router accumulates, preventing IP accounting from possibly consuming all available free memory. This level of memory consumption could occur in a router that is switching traffic for many hosts. Overflows will be recorded; see the monitoring commands for display formats.

The default accounting threshold of 512 entries results in a maximumn table size of 12928 bytes. Active and checkpointed tables can reach this size independently.

Example

The following example sets the IP accounting threshold to only 500 entries:

ip accounting-threshold 500
Related Commands

clear ip accounting
ip accounting
ip accounting-list
ip accounting-transits
show ip accounting

ip accounting-transits

To control the number of transit records that are stored in the IP accounting database, use the ip accounting-transits global configuration command. To return to the default number of records, use the no form of this command.

ip accounting-transits count
no ip accounting-transits

Syntax Description

count

Number of transit records to store in the IP accounting database.

Default

0

Command Mode

Global configuration

Usage Guidelines

Transit entries are those that do not match any of the filters specified by ip accounting-list global configuration commands. If no filters are defined, no transit entries are possible.

To maintain accurate accounting totals, the router software maintains two accounting databases: an active and a checkpointed database.

Example

The following example specifies that no more than 100 transit records are stored:

ip accounting-transit 100
Related Commands

clear ip accounting
ip accounting
ip accounting-list
ip accounting-threshold
show ip accounting

ip address

To set an IP address for an interface, use the ip address interface configuration command. To remove an IP address, use the no form of this command.

ip address ip-address mask
no
ip address ip-address mask

Syntax Description

ip-address

IP address.

mask

Mask for the associated IP subnet.

Default

No IP address is defined for an interface.

Command Mode

Interface configuration

Usage Guidelines

Hosts can determine subnet masks using the Internet Control Message Protocol (ICMP) Mask Request message. Routers respond to this request with an ICMP Mask Reply message.

You can disable IP processing on a particular interface by removing its IP address with the no ip address command. If the router detects another host using one of its IP addresses, it will print an error message on the console.

Example

In the following example, 131.108.1.27 is the primary address for Ethernet 0:

interface ethernet 0 ip address 131.108.1.27 255.255.255.0

ip address secondary

To set multiple IP addresses for an interface, use the ip address secondary interface configuration command. To remove an address, use the no form of this command.

ip address ip-address mask secondary
no
ip address ip-address mask secondary

Syntax Description

ip-address

IP address.

mask

Mask for the associated IP subnet.

Default

No secondary IP addresses are defined.

Command Mode

Interface configuration

Usage Guidelines

Hosts can determine subnet masks using the Internet Control Message Protocol (ICMP) Mask Request message. Routers respond to this request with an ICMP Mask Reply message.

Packets generated by the router always use the primary interface IP address. Therefore, all routers on a segment should share the same primary network number.


Note When you are routing OSPF, ensure that all secondary addresses of an interface fall into the same OSPF area as the primary addresses.
Example

In the following example, 131.108.1.27 is the primary address and 192.31.7.17 and 192.31.8.17 are secondary addresses for Ethernet 0:

interface ethernet 0 ip address 131.108.1.27 255.255.255.0 ip address 192.31.7.17 255.255.255.0 secondary ip address 192.31.8.17 255.255.255.0 secondary

ip broadcast-address

To define a broadcast address for an interface, use the ip broadcast-address interface configuration command. To restored the default IP broadcast address, use the no form of this command.

ip broadcast-address [ip-address]
no
ip broadcast-address [ip-address]

Syntax Description

ip-address

(Optional) IP broadcast address for a network.

Default

Default address: 255.255.255.255 (all ones)

Command Mode

Interface configuration

Example

The following example specifies an IP broadcast address of 0.0.0.0:

ip broadcast-address 0.0.0.0

ip cache-invalidate-delay

To control the invalidation rate of the IP route cache, use the ip cache-invalidate-delay global configuration command. To allow the IP route cache to be immediately invalidated, use the no form of this command.

ip cache-invalidate-delay [minimum maximum quiet threshold]
no
ip cache-invalidate-delay

Syntax Description

minimum

(Optional) Minimum time, in seconds, between invalidation request and actual invalidation. The default is 2 seconds.

maximum

(Optional) Maximum time, in seconds, between invalidation request and actual invalidation. The default is 5 seconds.

quiet

(Optional) Length of quiet period, in seconds, before invalidation.

threshold

(Optional) Maximum number of invalidation requests considered to be quiet.

Default

minimum = 2 seconds
maximum = 5 seconds, and 3 seconds with no more than zero invalidation requests

Command Mode

Global configuration

Usage Guidelines

All cache invalidation requests are honored immediately.

This command should typically not be used except under the guidance of technical support personnel. Incorrect settings can seriously degrade network performance.

The IP fast switching and autonomous switching features maintain a cache of IP routes for rapid access. When a packet is to be forwarded and the corresponding route is not present in the cache, the packet is process-switched and a new cache entry is built. However, when routing table changes occur (such as when a link or an interface goes down), the route cache must be flushed so that it can be rebuilt with up-to-date routing information.

This command controls how the route cache is flushed. The intent is to delay invalidation of the cache until after routing has settled down, since there tend to be many route table changes clustered in a short period of time, and the cache may be flushed repeatedly, which may put a high CPU load on the router.

When this feature is enabled, and the system requests that the route cache be flushed, the request is held for at least minimum seconds. Then the system determines whether the cache has been "quiet," that is, less than threshold invalidation requests in the last quiet seconds. If the cache has been quiet, the cache is then flushed. If the cache does not become quiet within maximum seconds after the first request, it is flushed unconditionally.

Manipulation of these parameters trades off CPU utilization versus route convergence time. Note that this does not affect the timing of the routing protocols, but only of the removal of stale cache entries.

Example

The following example sets a minimum delay of 5 seconds, a maximum delay of 30 seconds, and a quiet threshold of no more than 5 invalidation requests in the previous 10 seconds:

ip cache-invalidate-delay 5 30 10 5
Related Commands

ip route-cache
show ip cache

ip classless

At times the router might receive packets destined for a subnet of a network that has no network default route. To have the router forward such packets to the best supernet route possible, use the ip classless global configuration command. To disable this feature, use the no form of this command.

ip classless
no ip classless


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

This command allows the router to forward packets that are destined for unrecognized subnets of directly connected networks. By default, when a router receives packets for a subnet that numerically falls within its subnetwork addressing scheme, if there is no such subnet number in the routing table and there is no network default route, the router discards the packets. However, when the ip classless command is enabled, the router instead forwards those packets to the best supernet route.

Example

The following example configures the router to forward packets destined for an unrecognized subnet to the best supernet possible:

ip classless

ip default-gateway

To define a default gateway (router) when IP routing is disabled, use the ip default-gateway global configuration command. To disable this function, use the no form of this command.

ip default-gateway ip-address
no ip default-gateway ip-address

Syntax Description

ip-address

IP address of the router.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

The router sends any packets that need the assistance of a gateway to the address you specify. If another gateway has a better route to the requested host, the default gateway sends an ICMP redirect message to the router. The ICMP redirect message indicates which local router the router should use.

Example

The following example defines the router on IP address 192.31.7.18 as the default router:

ip default-gateway 192.31.7.18
Related Command

show ip redirects

ip directed-broadcast

To enable the translation of directed broadcast to physical broadcasts, use the ip directed-broadcast interface configuration command. To disable this function, use the no form of this command.

ip directed-broadcast [access-list-number]
no
ip directed-broadcast [access-list-number]

Syntax Description

access-list-number

(Optional) Number of the access list. If specified, a broadcast must pass the access list to be forwarded. If not specified, all broadcasts are forwarded.

Default

Enabled, with no list specified

Command Mode

Interface configuration

Usage Guidelines

This feature is enabled only for those protocols configured using the ip forward-protocol global configuration command. An access list may be specified to control which broadcasts are forwarded. When an access list is specified, only those IP packets permitted by the access list are eligible to be translated from directed broadcasts to physical broadcasts.

Example

The following example enables forwarding of IP directed broadcasts on interface Ethernet 0:

interface ethernet 0 ip directed-broadcast
Related Command

ip forward-protocol

ip domain-list

To define a list of default domain names to complete unqualified host names (in this command, names that do not end with a dot), use the ip domain-list global configuration command. To delete a name from a list, use the no form of this command.

ip domain-list name
no ip domain-list name

Syntax Description

name

Domain name. Do not include the initial period that separates an unqualified name from the domain name.

Default

No domain names are defined.

Command Mode

Global configuration

Usage Guidelines

If there is no domain list, the domain name that you specified with the ip domain-name global configuration command is used. If there is a domain list, the default domain name is not used. The ip domain-list command is similar to the ip domain-name command, except that with ip domain-list you can define a list of domains, each to be tried in turn.

The ip domain-list command considers a name to be fully qualified only if that name ends in a dot. Significantly, the ip domain name command considers a name to be fully qualified if it contains a dot anywhere in the name.

Examples

The following example adds several domain names to a list:

ip domain-list martinez.com ip domain-list stanford.edu

The following example adds a name to and then deletes a name from the list:

ip domain-list sunya.edu no ip domain-list stanford.edu
Related Command

ip domain-name

Default

No domain names are defined.

Command Mode

Global configuration

Usage Guidelines

If there is no domain list, the domain name that you specified with the ip domain-name global configuration command is used. If there is a domain list, the default domain name is not used. The ip domain-list command is similar to the ip domain-name command, except that with ip domain-list you can define a list of domains, each to be tried in turn.

The ip domain-list command considers a name to be fully qualified only if that name ends in a dot. Significantly, the ip domain name command considers a name to be fully qualified if it contains a dot anywhere in the name.

Examples

The following example adds several domain names to a list:

ip domain-list martinez.com ip domain-list stanford.edu

The following example adds a name to and then deletes a name from the list:

ip domain-list sunya.edu no ip domain-list stanford.edu
Related Command

ip domain-name

ip domain-lookup

To enable the IP Domain Name System-based host name-to-address translation, use the ip domain-lookup global configuration command. To disable the Domain Name System, use the no form of this command.

ip domain-lookup
no ip domain-lookup


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Global configuration

Example

The following example enables the IP Domain Name System-based host name-to-address translation:

ip domain-lookup
Related Commands

ip domain-lookup nsap
ip domain-name
ip name-server

ip domain-lookup nsap

To allow Domain Name System (DNS) queries for CLNS addresses, use the ip domain-lookup nsap global configuration command. To disable this feature, use the no form of this command.

ip domain-lookup nsap
no ip domain-lookup nsap


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Global configuration

Usage Guidelines

With both IP and ISO CLNS enabled on a router, this feature allows the router to dynamically determine a CLNS address given a host name. This feature is useful for the ISO CLNS ping EXEC command and when making CLNS Telnet connections.

Example

The following example disables DNS queries of CLNS addresses:

no ip domain-lookup nsap
Related Commands

A dagger (†) indicates that the command is documented in another chapter.

ip domain-lookup
ping
(for ISO CLNS)

ip domain-name

To define a default domain name that the Cisco IOS software uses to complete unqualified host names (in this command, names without dots in the name), use the ip domain-name global configuration command. To disable, use the no form of this command.

ip domain-name name
no ip domain-name

Syntax Description

name

Default domain name used to complete unqualified host names. Do not include the initial period that separates an unqualified name from the domain name.

Default

No domain name is defined.

Command Mode

Global configuration

Usage Guidelines

Any IP host name with an unqualified domain name (any name without a dot), will have the dot and the defined name appended to it before being added to the host table. Any IP host name that ends in a dot will not have the dot and the defined name appended to it, because the system considers any name containing a dot to be a fully-qualified domain name.

The ip domain name command considers a name to be fully-qualified if it contains a dot anywhere in the name. Significantly, the ip domain-list command considers a name to be fully qualified only if that name ends in a dot.

Examples

The following example defines cisco.com as the default domain name:

ip domain-name cisco.com

The following example would not append the default domain name to the entered name before querying the DNS server because the name appears to be a fully-qualified domain name.

router>ping sales.marketing
Related Commands

ip domain-list
ip domain-lookup
ip name-server

ip forward-protocol

To specify which protocols and ports the router forwards when forwarding broadcast packets, use the ip forward-protocol global configuration command. To remove a protocol or port, use the no form of this command.

ip forward-protocol {udp [port] | nd | sdns}
no ip forward-protocol {udp [port] | nd | sdns}

Syntax Description

udp

Forward User Datagram Protocol (UDP) datagrams. See the "Default" section below for a list of port numbers forwarded by default.

port

(Optional) Destination port that controls which UDP services are forwarded.

nd

Forward Network Disk (ND) datagrams. This protocol is used by older diskless SUN workstations.

sdns

Secure Data Network Service.

Default

If an IP helper address is defined, UDP forwarding is enabled on default ports. If UDP flooding is configured, UDP flooding is enabled on the default ports.

If a helper address is specified and UDP forwarding is enabled, broadcast packets destined to the following port numbers are forwarded by default:


Note Using the ip directed-broadcast interface configuration command with the optional access-list-number argument overrides the behavior of teh ip forward-protocol command.
Command Mode

Global configuration

Usage Guidelines

Enabling a helper address or UDP flooding on an interface causes the router to forward particular broadcast packets. You can use the ip forward-protocol command to specify exactly which types of broadcast packets you would like to have forwarded. A number of commonly forwarded applications are enabled by default. Enabling forwarding for some ports (for example, RIP) may be hazardous to your network.

If you use the ip forward-protocol command, specifying just UDP, without the port, enables forwarding and flooding on the default ports.

One common application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP). DHCP is defined in RFC 1531. DHCP protocol information is carried inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server. If you have multiple servers, you can configure one helper address for each server. Since BOOTP packets are forwarded by default, DHCP information can now be forwarded by the router. The DHCP server now receives broadcasts from the DHCP clients.

Example

The following example uses the ip forward-protocol command to specify forwarding of UDP port 3001 in addition to the default ports, and then defines a helper address:

ip forward-protocol udp 3001 ! interface ethernet 1 ip helper-address 131.120.1.0
Related Commands

ip directed-broadcast
ip forward-protocol spanning-tree
ip forward-protocol turbo-flood
ip helper-address

ip forward-protocol any-local-broadcast

To forward any broadcasts including local subnet broadcasts, use the ip forward-protocol any-local-broadcast global configuration command. To disable this type of forwarding, use the no form of this command.

ip forward-protocol any-local-broadcast
no ip forward-protocol any-local-broadcast


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

The ip forward-protocol any-local-broadcast command forwards packets similarly to how theip forward-protocol spanning-tree command does. That is, it forwards packets whose contents are all ones (255.255.255.255), all zeros (0.0.0.0), and, if subnetting is enabled, all networks (131.108.255.255 as an example in the network number 131.108.0.0. This mechanism also forwards packets whose contents are the zeros version of the all-networks broadcast when subnetting is enabled (for example, 131.108.0.0). In addition, it forwards any local subnet broadcast packets.

Example

Assume a router is directly connected to subnet 1 of network 131.108.0.0 and that the netmask is 255.255.255.0. The following command enables the forwarding of IP broadcasts destined to 131.108.1.255 and 131.108.1.0 in addition to the broadcast addresses mentioned in the "Usage Guidelines" section:

ip forward-protocol any-local-broadcast
Related Command

ip forward-protocol spanning-tree

ip forward-protocol spanning-tree

To permit IP broadcasts to be flooded throughout the internetwork in a controlled fashion, use the ip forward-protocol spanning-tree global configuration command. To disable the flooding of IP broadcasts, use the no form of this command.

ip forward-protocol spanning-tree
no ip forward-protocol spanning-tree


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

Packets must meet the following criteria to be considered for flooding:

A flooded UDP datagram is given the destination address specified by the ip broadcast-address interface configuration command on the output interface. The destination address can be set to any desired address. Thus, the destination address may change as the datagram propagates through the network. The source address is never changed. The TTL value is decremented.

After a decision has been made to send the datagram out on an interface (and the destination address possibly changed), the datagram is handed to the normal IP output routines and is therefore subject to access lists, if they are present on the output interface.

The ip forward-protocol spanning-tree command uses the database created by the bridging spanning-tree protocol. Therefore, the transparent bridging option must be in the routing software, and bridging must be configured on each interface that is to participate in the flooding in order to support this capability.

If an interface does not have bridging configured, it still will be able to receive broadcasts, but it will never forward broadcasts received on that interface, and it will never use that interface to send broadcasts received on a different interface.

If no actual bridging is desired, you can configure a type-code bridging filter that will deny all packet types from being bridged. Refer to the Transparent Bridging chapter in the Router Products Configuration Guide for more information about using access lists to filter bridged traffic. The spanning-tree database is still available to the IP forwarding code to use for the flooding.

The spanning-tree-based flooding mechanism fowards packets whose contents are all ones (255.255.255.255), all zeros (0.0.0.0), and, if subnetting is enabled, all networks (131.108.255.255 as an example in the network number 131.108.0.0. This mechanism also forward packets whose contents are the zeros version of the all-networks braodcast when subnetting is enabled (for example, 131.108.0.0).

This command is an extension of the ip helper-address interface configuration command, in that the same packets that may be subject to the helper address and forwarded to a single network can now be flooded. Only one copy of the packet will be put on each network segment.

Example

The following example permits IP broadcasts to be flooded through the internetwork in a controlled fashion:

ip forward-protocol spanning-tree
Related Commands

ip broadcast-address
ip helper-address
ip forward-protocol
ip forward-protocol turbo-flood

ip forward-protocol turbo-flood

To speed up flooding of User Datagram Protocol (UDP) datagrams using the spanning-tree algorithm, use the ip forward-protocol turbo-flood global configuration command. To disable this feature, use the no form of this command.

ip forward-protocol turbo-flood
no ip forward-protocol turbo-flood


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

Used in conjunction with the ip forward-protocol spanning-tree global configuration command, this feature is supported over ARPA-encapsulated Ethernets, FDDI, and HDLC-encapsulated serials, but is not supported on Token Rings. As long as the Token Rings and the non-HDLC serials are not part of the bridge group being used for UDP flooding, turbo flooding will behave normally.

Example

The following is an example of a two-port router (2E) using this feature:

ip forward-protocol turbo-flood ip forward-protocol spanning-tree ! interface ethernet 0 ip address 128.9.1.1 bridge-group 1 ! interface ethernet 1 ip address 128.9.1.2 bridge-group 1 ! ! bridge 1 protocol dec
Related Commands

ip forward-protocol
ip forward-protocol spanning-tree

ip gdp gdp

To configure the router discovery feature using the Cisco Gateway Discovery Protocol (GDP) routing protocol, use the ip gdp gdp interface configuration command. To disable this feature, use the no form of this command.

ip gdp gdp
no ip gdp gdp


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

IP routing must be disabled before you can configure this feature.

Example

The following example configures router discovery using GDP on Ethernet interface 0:

interface ethernet 0 ip gdp gdp

ip gdp igrp

To configure the router discovery feature using the Cisco Interior Gateway Routing Protocol (IGRP), use the ip gdp igrp interface configuration command. To disable this feature, use the no form of this command.

ip gdp igrp
no ip gdp igrp


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

IP routing must be disabled before you can configure this feature.

Example

The following example configures router discovery using IGRP on Ethernet interface 1:

interface ethernet 1 ip gdp igrp

ip gdp irdp

To configure the router discovery feature using the ICMP Router Discovery Protocol (IRDP), use the ip gdp irdp interface configuration command. To disable this feature, use the no form of this command.

ip gdp irdp
no ip gdp irdp


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

IP routing must be disabled before you can configure this feature.

Example

The following example configures router discovery using IRDP on Ethernet interface 0:

interface ethernet 0 ip gdp irdp

ip gdp rip

To configure the router discovery feature using the Routing Information Protocol (RIP), use the ip gdp rip interface configuration command. To disable this feature, use the no form of this command.

ip gdp rip
no ip gdp rip


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

IP routing must be disabled before you can configure this feature.

Example

The following example configures router discovery using RIP on Ethernet interface 1:

interface ethernet 1 ip gdp rip

ip helper-address

To have the router forward User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface, use the ip helper-address interface configuration command. To disable the forwarding of broadcast packets to specific addresses, use the no form of this command.

ip helper-address address
no ip helper-address address

Syntax Description

address

Destination broadcast or host address to be used when forwarding UDP broadcasts. You can have more than one helper address per interface.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

Combined with the ip forward-protocol global configuration command, the ip helper-address command allows you to control which broadcast packets and which protocols are forwarded.

One common application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP). DHCP is defined in RFC 1531. DHCP protocol information is carried inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server. If you have multiple servers, you can configure one helper address for each server. Since BOOTP packets are forwarded by default, DHCP information can now be forwarded by the router. The DHCP server now receives broadcasts from the DHCP clients.

Example

The following example defines an address that acts as a helper address:

interface ethernet 1 ip helper-address 121.24.43.2
Related Command

ip forward-protocol

ip host

To define a static host name-to-address mapping in the host cache, use the ip host global configuration command. To remove the name-to-address mapping, use the no form of this command.

ip host name [tcp-port-number] address1 [address2...address8]
no ip host name address

Syntax Description

name

Name of the host. The first character can be either a letter or a number, but if you use a number, the operations you can perform are limited.

tcp-port-number

(Optional) TCP port number to connect to when using the defined host name in conjunction with an EXEC connect or telnet command. The default is Telnet (port 23).

address1

Associated IP address.

address2...address8

(Optional) Additional associated IP address. You can bind up to eight addresses to a host name.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

The first character can be either a letter or a number, but if you use a number, the operations you can perform (such as ping) are limited.

Example

The following example uses the ip host command to define two static mappings:

ip host croff 192.31.7.18 ip host bisso-gw 10.2.0.2 192.31.7.33

ip hp-host

To enter into the host table the host name of an HP host to be used for HP Probe Proxy service, use the ip hp-host global configuration command. To remove a host name, use the no form of this command.

ip hp-host hostname ip-address
no ip hp-host hostname ip-address

Syntax Description

hostname

Name of the host.

ip-address

IP address of the host.

Default

No host names are defined.

Command Mode

Global configuration

Usage Guidelines

To use the HP Proxy service, you must first enter the host name of the HP host into the host table using this command.

Example

The following example specifies an HP host's name and address, and then enables Probe Proxy:

ip hp-host BCWjo 131.108.1.27 interface ethernet 0 ip probe proxy
Related Command

ip probe proxy

ip mask-reply

To have the router to respond to Internet Control Message Protocol (ICMP) mask requests by sending ICMP Mask Reply messages, use the ip mask-reply interface configuration command. To disable this function, use the no form of this command.

ip mask-reply
no ip mask-reply


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Example

The following example enables the sending of ICMP Mask Reply messages on interface Ethernet 0:

interface ethernet 0 ip address 131.108.1.0 255.255.255.0 ip mask-reply

ip mobile arp

To enable local-area mobility, use the ip mobile arp interface configuration command. To disable local-area mobility, use the no form of this command.

ip mobile arp [timers keepalive hold-time] [access-group access-list-number]
no ip mobile arp [timers keepalive hold-time] [access-group access-list-number]


Syntax Description

timers

(Optional) Indicates that you are setting local-area mobility timers.

keepalive

(Optional) Frequency, in seconds, at which the router sends unicast ARP messages to a relocated host to verify that the host is present and has not moved. The default keepalive time is 300 seconds (5 minutes).

hold-time

(Optional) Hold time, in seconds. This is the length of time the router considers that a relocated host is present without receiving some type of ARP broadast or unicast from the host. Normally, the hold time should be at least three times greater than the keepalive time. The default hold time is 900 seconds (15 minutes).

access-group

(Optional) Indicates that you are applying an access list. This access list applies only to local-area mobility.

access-list-number

(Optional) Number of a standard IP access list. It is a decimal number from 1 to 99. Only hosts with addresses permitted by this access list are accepted for local-area mobility.

Default

Local-area mobility is disabled.

If you enable local-area mobility:
keepalive: 300 seconds (5 minutes)
hold-time: 900 seconds (15 minutes)

Command Mode

Interface configuration

Usage Guidelines

Local-area mobility is supported on Ethernet, Token Ring, and FDDI interfaces only.

To create larger mobility areas, you must first redistribute the mobile routes into your IGP. The IGP must support host routes. You can use Enhanced IGRP, OSPF, or ISIS; you can also use RIP, but this is not recommended. The mobile area must consist of a contiguous set of subnets.

Using an access list to control the list of possible mobile nodes is strongly encouraged. Without an access list, misconfigured hosts can be taken for mobile nodes and disrupt normal operations.

Example

The following example configures local-area mobility on Ethernet interface 0:

bridge 1 protocol ieee access-list 10 permit 198.92.37.114 interface ethernet 0 ip mobile arp access-group 10 bridge-group 1
Related Commands

A dagger (†) indicates that the command is documented in another chapter.

access-list (standard)
bridge-group

bridge protocol
default-metric (BGP, EGP, OSPF, and RIP)
network
redistribute
router eigrp
router isis
router ospf

ip mtu

To set the maximum transmission unit (MTU) size of IP packets sent on an interface, use the ip mtu interface configuration command. To restore the default MTU size, use the no form of this command.

ip mtu bytes
no ip mtu

Syntax Description

bytes

MTU in bytes.

Default

Minimum is 128 bytes; maximum depends on interface medium.

Command Mode

Interface configuration

Usage Guidelines

If an IP packet exceeds the MTU set for the router's interface, the router will fragment it.

All devices on a physical medium must have the same protocol MTU in order to operate.


Note Changing the MTU value (with the mtu interface configuration command) can affect the IP MTU value. If the current IP MTU value is the same as the MTU value, and you change the MTU value, the IP MTU value will be modified automatically to match the new MTU. However, the reverse is not true; changing the IP MTU value has no effect on the value for the mtu command.
Example

The following example sets the maximum IP packet size for the first serial interface to 300 bytes:

interface serial 0 ip mtu 300
Related Command

A dagger (†) indicates that the command is documented in another chapter.

mtu

ip name-server

To specify the address of one or more name servers to use for name and address resolution, use the ip name-server global configuration command. To remove the addresses specified, use the no form of this command.

ip name-server server-address1 [[server-address2]... server-address6]
no ip name-server
server-address1 [[server-address2]... server-address6]

Syntax Description

server-address1

IP addresses of name server.

server-address2...server-address6

(Optional) IP addresses of additional name servers (a maximum of six name servers).

Default

No name server addresses are specified.

Command Mode

Global configuration

Example

The following example specifies host 131.108.1.111 as the primary name server and host 131.108.1.2 as the secondary server:

ip name-server 131.108.1.111 131.108.1.2

This command will be reflected in the configuration file as follows:

ip name-server 131.108.1.111 ip name-server 131.108.1.2
Related Commands

ip domain-lookup
ip domain-name

ip netmask-format

To specify the format in which netmasks are displayed in show command output, use the ip netmask-format line configuration command. To restore the default display format, use the no form of this command.

ip netmask-format {bitcount | decimal | hexadecimal}
no ip netmask-format [bitcount | decimal | hexadecimal]

Syntax Description

bitcount

Addresses are followed by a slash and the total number of bits in the netmask. For example, 131.108.11.0/24 indicates that the netmask is 24 bits.

decimal

Network masks are displayed in dotted decimal notation (for example, 255.255.255.0).

hexadecimal

Network masks are displayed in hexadecimal format, as indicated by the leading 0X (for example, 0XFFFFFF00).

Default

Netmasks are displayed in dotted decimal format.

Command Mode

Line configuration

Usage Guidelines

IP uses a 32-bit mask that indicates which address bits belong to the network and subnetwork fields and which bits belong to the host field. This is called a netmask. By default, show commands display an IP address and then its netmask in dotted decimal notation. For example, a subnet would be displayed as 131.108.11.0 255.255.255.0.

However, you can specify that the display of the network mask appear in hexadecimal format or bit count format instead. The hexadecimal format is commonly used on UNIX systems. The above example would be displayed as 131.108.11.0 0XFFFFFF00.

The bitcount format for displaying network masks is to append a slash (/) and the total number of bits in the netmask to the address itself. The above example would be displayed as 131.108.11.0/24.

Example

The following example configures network masks for the specified line to be displayed in bitcount notation in the output of show commands:

line vty 0 4 ip netmask-format bitcount

ip nhrp authentication

To configure the authentication string for an interface using Next Hop Resolution Protocol (NHRP), use the ip nhrp authentication interface configuration command. To remove the authentication string, use the no form of this command.

ip nhrp authentication string
no ip nhrp authentication [string]

Syntax Description

string

Authentication string configured for the source and destination stations that controls whether NHRP stations allow intercommunication. The string can be up to 8 characters long.

Default

No authentication string is configured; the router adds no authentication option to NHRP packets it generates.

Command Mode

Interface configuration

Usage Guidelines

All routers configured with NHRP on a fabric (for an interface) must share the same authentication string.

Example

In the following example, the authentication string specialxx must be configured in all routers using NHRP on the interface before NHRP communication occurs:

ip nhrp authentication specialxx

ip nhrp holdtime

To change the number of seconds that NHRP nonbroadcast, multiaccess (NBMA) addresses are advertised as valid in authoritative NHRP responses, use the ip nhrp holdtime interface configuration command. To restore the default value, use the no form of this command.

ip nhrp holdtime seconds-positive [seconds-negative]
no ip nhrp holdtime [seconds-positive [seconds-negative]]

Syntax Description

seconds-positive

Time in seconds that NBMA addresses are advertised as valid in positive authoritative NHRP responses.

seconds-negative

(Optional) Time in seconds that NBMA addresses are advertised as valid in negative authoritative NHRP responses.

Default

7200 seconds (2 hours) for both arguments

Command Mode

Interface configuration

Usage Guidelines

The ip nhrp holdtime command affects authoritative responses only. The advertised holding time is the length of time the router tells other routers to keep information that it is providing in authoritative NHRP responses. The cached IP-to-NBMA address mapping entries are discarded after the holding time expires.

The NHRP cache can contain static and dynamic entries. The static entries never expire. Dynamic entries expire regardless of whether they are authoritative or nonauthoritative.

If you want to change the valid time period for negative NHRP responses, you must also include a value for positive NHRP responses, as the arguments are position dependent.

Examples

In the following example, NHRP NBMA addresses are advertised as valid in positive authoritative NHRP responses for one hour:

ip nhrp holdtime 3600

In the following example, NHRP NBMA addresses are advertised as valid in negative authoritative NHRP responses for one hour and in positive authoritative NHRP responses for two hours:

ip nhrp holdtime 7200 3600

ip nhrp interest

To control which IP packets can trigger sending a Next Hop Resolution Protocol (NHRP) Request, use the ip nhrp interest interface configuration command. To restore the default value, use the no form of this command.

ip nhrp interest access-list-number
no ip nhrp interest [access-list-number]

Syntax Description

access-list-number

Standard or extended IP access list number in the range 1 through 199.

Default

All non-NHRP packets can trigger NHRP requests.

Command Mode

Interface configuration

Usage Guidelines

Use this command with the access-list command to control which IP packets trigger NHRP Requests.

Example

In the following example, any TCP traffic can cause NHRP Requests to be sent, but no other IP packets will cause NHRP Requests:

ip nhrp interest 101 access-list 101 permit tcp any any
Related Commands

access-list (standard)
access-list (extended)

ip nhrp map

To statically configure the IP-to-NBMA address mapping of IP destinations connected to a nonbroadcast, multiaccess (NBMA) network, use the ip nhrp map interface configuration command. To remove the static entry from NHRP cache, use the no form of this command.

ip nhrp map ip-address nbma-address
no ip nhrp map ip-address nbma-address

Syntax Description

ip-address

IP address of the destinations reachable through the NBMA network. This address is mapped to the NBMA address.

nbma-address

Nonbroadcast, multiaccess (NBMA) address which is directly reachable through the NBMA network. The address format varies depending on the medium you are using. For example, ATM has an NSAP address, Ethernet has a MAC address, and SMDS has an E.164 address. This address is mapped to the IP address.

Default

No static IP-to-NBMA cache entries exist.

Command Mode

Interface configuration

Usage Guidelines

You will probably have to configure at least one static mapping in order to reach the Next Hop Server. Repeat this command to statically configure multiple IP-to-NBMA address mappings.

Example

In the following example, this station in a multipoint tunnel network is statically configured to be served by two Next Hop Servers 100.0.0.1 and 100.0.1.3. The NBMA address for 100.0.0.1 is statically configured to be 11.0.0.1 and the NBMA address for 100.0.1.3 is 12.2.7.8.

interface tunnel 0 ip nhrp nhs 100.0.0.1 ip nhrp nhs 100.0.1.3 ip nhrp map 100.0.0.1 11.0.0.1 ip nhrp map 100.0.1.3 12.2.7.8
Related Command

clear ip nhrp

ip nhrp map multicast

To configure NBMA addresses used as destinations for broadcast or multicast packets to be sent over a tunnel network, use the ip nhrp map multicast interface configuration command. To remove the destinations, use the no form of this command.

ip nhrp map multicast nbma-address
no ip nhrp map multicast nbma-address

Syntax Description

nbma-address

Nonbroadcast, multiaccess (NBMA) address which is directly reachable through the NBMA network. The address format varies depending on the medium you are using.

Default

No NBMA addresses are configured as destinations for broadcast or multicast packets.

Command Mode

Interface configuration

Usage Guidelines

This command applies to tunnel interfaces only.

This command is useful for supporting broadcasts over a tunnel network when the underlying network does not support IP multicast. If the underlying network does support IP multicast, you should use the tunnel destination command to configure a multicast destination for transmission of tunnel broadcasts or multicasts.

When multiple NBMA addresses are configured, the system replicates the broadcast packet for each address.

Example

In the following example, if a packet is sent to 10.255.255.255, it is replicated to destinations 11.0.0.1 and 11.0.0.2. Addresses 11.0.0.1 and 11.0.0.2 are the IP addresses of two other routers that are part of the tunnel network, but those addresses are their addresses in the underlying network, not the tunnel network. They would have tunnel addresses that are in network 10.0.0.0.

interface tunnel 0 ip address 10.0.0.3 255.0.0.0 ip nhrp map multicast 11.0.0.1 ip nhrp map multicast 11.0.0.2

ip nhrp network-id

To enable the Next Hop Resolution Protocol (NHRP) on an interface, use the ip nhrp network-id interface configuration command. To disable NHRP on the interface, use the no form of this command.

ip nhrp network-id number
no ip nhrp network-id [number]

Syntax Description

number

Globally-unique, 32-bit network identifier for a nonbroadcast, multiaccess (NBMA) network. The range is 1 to 4294967295.

Default

NHRP is disabled on the interface.

Command Mode

Interface configuration

Usage Guidelines

In general, all NHRP stations within a fabric must be configured with the same network identifier.

Example

In the following example, NHRP is enabled on the interface:

ip nhrp network-id 1

ip nhrp nhs

To specify the address of one or more NHRP Next Hop Servers, use the ip nhrp nhs interface configuration command. To remove the address, use the no form of this command.

ip nhrp nhs nhs-address [net-address [netmask]]
no ip nhrp nhs nhs-address [net-address [netmask]]

Syntax Description

nhs-address

Address of the Next Hop Server being specified.

net-address

(Optional) IP address of a network served by the Next Hop Server.

netmask

(Optional) IP network mask to be associated with the net IP address. The net IP address is logically ANDed with the mask.

Default

No Next Hop Servers are explicitly configured, so NHRP fabric mode is assumed and normal IP routing decisions are used to forward NHRP traffic.

Command Mode

Interface configuration

Usage Guidelines

Use this command to specify the address of a Next Hop Server and the networks it serves. When Next Hop Servers are configured, server mode is assumed. In server mode, each Next Hop Server should be configured with information as to what networks are served by the other Next Hop Servers in the nonbroadcast, multiaccess (NBMA) network.

For any Next Hop Server that is configured, you can specify multiple networks that it serves by repeating this command with the same nhs-address address, but different net-address IP network addresses.

If no Next Hop Server is configured for an NBMA network, NHRP fabric mode is assumed.

Example

In the following example, the Next Hop Server with address 131.108.10.11 serves IP network 10.0.0.0. The mask is 255.0.0.0.

ip nhrp nhs 131.108.10.11 10.0.0.0 255.0.0.0

ip nhrp record

To re-enable the use of forward record and reverse record options in NHRP Request and Reply packets, use the ip nhrp record interface configuration command. To suppress the use of such options, use the no form of this command.

ip nhrp record
no ip nhrp record


Syntax Description

This command has no arguments or keywords.

Default

Forward record and reverse record options are used in NHRP Request and Reply packets.

Command Mode

Interface configuration

Usage Guidelines

Forward record and reverse record options provide loop detection and are enabled by default. Using the no form of this command disables this method of loop detection. For another method of loop detection, see the ip nhrp responder command.

Example

In the following example, forward record and reverse record options are suppressed:

no ip nhrp record
Related Command

ip nhrp responder

ip nhrp responder

To designate which interface's primary IP address the Next Hop Server will use in NHRP Reply packets when the NHRP requestor uses the Responder Address option, use the ip nhrp responder interface configuration command. To remove the designation, use the no form of this command.

ip nhrp responder type number
no ip nhrp responder [type] [number]

Syntax Description

type

Interface type whose primary IP address is used when a Next Hop Server complies with a Responder Address option (for example, serial, tunnel).

number

Interface number whose primary IP address is used when a Next Hop Server complies with a Responder Address option.

Default

The Next Hop Server uses the IP address of the interface where the NHRP Request was received.

Command Mode

Interface configuration

Usage Guidelines

If an NHRP requestor wants to know which Next Hop Server generates an NHRP Reply packet, it can request that information through the Responder Address option. The Next Hop Server that generates the NHRP Reply packet then complies by inserting its own IP address in the Responder Address option of the NHRP Reply. The Next Hop Server uses the primary IP address of the specified interface.

If an NHRP Reply packet being forwarded by a Next Hop Server contains that Next Hop Server's own IP address, the Next Hop Server generates an Error Indication of type "NHRP Loop Detected" and discards the Reply.

Example

In the following example, any NHRP requests for the Responder Address will cause this router acting as a Next Hop Server to supply the primary IP address of serial interface 0 in the NHRP Reply packet:

ip nhrp responder serial 0

ip probe proxy

To enable the HP Probe Proxy support, which allows a router to respond to HP Probe Proxy Name requests, use the ip probe proxy interface configuration command. To disable HP Prove Proxy, use the no form of this command.

ip probe proxy
no ip probe proxy


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

HP Probe Proxy Name requests are typically used at sites that have HP equipment and are already using HP Probe.

To use the HP Proxy service, you must first enter the host name of the HP host into the host table using the ip hp-host global configuration command.

Example

The following example specifies an HP host's name and address, and then enables Probe Proxy:

ip hp-host BCWjo 131.108.1.27 interface ethernet 0 ip probe proxy
Related Command

ip hp-host

ip proxy-arp

To enable proxy ARP on an interface, use the ip proxy-arp interface configuration command. To disable proxy ARP on the interface, use the no form of this command.

ip proxy-arp
no ip proxy-arp


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Interface configuration

Example

The following example enables proxy ARP on Ethernet interface 0:

interface ethernet 0 ip proxy-arp

ip redirects

To enable the sending of redirect messages if the router is forced to resend a packet through the same interface on which it was received, use the ip redirects interface configuration command. To disable the sending of redirect messages, use the no form of this command.

ip redirects
no ip redirects


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Interface configuration

Example

The following example enables the sending of IP redirects on Ethernet interface 0:

interface ethernet 0 ip redirects
Related Command

show ip redirects

ip route-cache

To control the use of a high-speed switching cache for IP routing as well as the use of autonomous switching, use the ip route-cache interface configuration command. To disable fast switching and autonomous switching, use the no form of this command.

ip route-cache [cbus]
no ip route-cache [cbus]

ip route-cache same-interface
no ip route-cache same-interface


ip route-cache sse
no ip route-cache sse


Syntax Description

cbus

(Optional) Enables both autonomous switching and fast switching.

same-interface

Enables fast switching packets back out the interface on which they arrived.

sse

Enables SSE switching on the SSP board on the Cisco 7000 series.

Default

IP autonomous switching is disabled.
Fast switching varies by interface and media.
SSE switching of IP is disabled.

Command Mode

Interface configuration

Usage Guidelines

Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis.

The ip route-cache command with not additional keywords, enables fast switching.

Our routers generally offer better packet transfer performance when fast switching is enabled, with one exception. On networks using slow serial links (64K and below), disabling fast switching to enable the per-packet load sharing is usually the best choice.

Autonomous switching gives a router faster packet processing by allowing the ciscoBus to switch packets independently without interrupting the system processor. It works only in Cisco 7000 series or AGS+ systems with high-speed network controller cards, and with a switch processor or ciscoBus controller card running microcode Version 1.4 or later.

You can enable IP fast switching when the input and output interfaces are the same interface, using the ip route-cache same-interface command. This normally is not recommended, though it is useful when you have partially meshed media, such as Frame Relay. You could use this feature on other interfaces, although it is not recommended because it would interfere with redirection.

SSE switching gives a router even faster packet processing than the is provided by the other ip route-cache commands by allowing the SSE to switch packets without interrupting the system processor. SSE switching is supported only in Cisco 7000 systems with an SSP board. Fast switching must be active to enable SSE switching. SSE switching requires that fast switching be enabled.

Examples

The following example enables both fast switching and autonomous switching:

ip route-cache cbus

The following example disables both fast switching and autonomous switching:

no ip route-cache

The following example turns off autonomous switching only:

no ip route-cache cbus

The following example returns the system to its defaults (fast switching enabled; autonomous switching disabled):

ip route-cache
Related Commands

ip cache-invalidate-delay
show ip cache

ip routing

To enable IP routing on the router, use the ip routing global configuration command. To disable IP routing on the router, use the no form of this command.

ip routing
no ip routing


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Global configuration

Usage Guidelines

If the system is running bridging software, the no ip routing command turns off IP routing when setting up a system to bridge (as opposed to route) IP packets.

Example

The following example shows how to enable IP routing:

ip routing

ip security add

To add a basic security option to all outgoing packets, use the ip security add interface configuration command. To disable the adding of a basic security option to all outgoing packets, use the no form of this command.

ip security add
no ip security add


Syntax Description

This command has no arguments or keywords.

Default

Disabled, when the security level of the interface is "Unclassified Genser" (or unconfigured). Otherwise, the default is enabled.

Command Mode

Interface configuration

Usage Guidelines

If an outgoing packet does not have a security option present, this interface configuration command will add one as the first IP option. The security label added to the option field is the label that was computed for this packet when it first entered the router. Because this action is performed after all the security tests have been passed, this label will either be the same as or will fall within the range of the interface.

Example

The following example adds a basic security option to each packet leaving Ethernet interface 0:

interface ethernet 0 ip security add
Related Commands

ip security dedicated
ip security extended-allowed
ip security first
ip security ignore-authorities
ip security implicit-labelling
ip security multilevel
ip security reserved-allowed
ip security strip

ip security aeso

To attach Auxiliary Extended Security Options (AESOs) to an interface, use the ip security aeso command. To disable AESO on an interface, use the no form of this command.

ip security aeso source compartment-bits
no ip security aeso source compartment-bits

Syntax Description

source

Extended Security Option (ESO) source. This can be an integer from 0 through 255.

compartment-bits

Compartment bits in hexadecimal.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

Compartment bits are specified only if this AESO is to be inserted in a packet. On every incoming packet at this level on this interface, these AESOs should be present.

Beyond being recognized, no further processing of AESO information is performed. AESO contents are not checked and are assumed to be valid if the source is listed in the configurable AESO table.

Configuring any per-interface extended IP security option (IPSO) information automatically enables ip security extended-allowed (disabled by default).

Example

In the following example, the extended security option source is defined as 5 and the compartments bits are set to 5.

interface ethernet 0 ip security aeso 5 5
Related Commands

ip security eso-info
ip security eso-max
ip security eso-min
ip security extended-allowed

ip security dedicated

To set the level of classification and authority on the interface, use the ip security dedicated interface configuration command. To reset the interface to the default classification and authorities, use the no form of this command.

ip security dedicated level authority [authority...]
no ip security dedicated level authority [authority...]

Syntax Description

level

Degree of sensitivity of information. The level keywords are listed in Table 17-1.

authority

Organization that defines the set of security levels that will be used in a network. The authority keywords are listed in Table 17-2.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

All traffic entering the system on this interface must have a security option that exactly matches this label. Any traffic leaving via this interface will have this label attached to it.

The following definitions apply to the descriptions of the IP security options (IPSO) in this section:


Table 17-1: IPSO Level Keywords and Bit Patterns
Level Keyword Bit Pattern

Reserved4

0000 0001

TopSecret

0011 1101

Secret

0101 1010

Confidential

1001 0110

Reserved3

0110 0110

Reserved2

1100 1100

Unclassified

1010 1011

Reserved1

1111 0001


Table 17-2: IPSO Authority Keywords and Bit Patterns
Authority Keyword Bit Pattern

Genser

1000 0000

Siop-Esi

0100 0000

DIA

0010 0000

NSA

0001 0000

DOE

0000 1000

Example

The following example sets a confidential level with Genser authority:

ip security dedicated confidential Genser
Related Commands

ip security add
ip security extended-allowed
ip security first
ip security ignore-authorities
ip security implicit-labelling
ip security multilevel
ip security reserved-allowed
ip security strip

ip security eso-info

To configure system-wide defaults for extended IP Security Option (IPSO) information, use the ip security eso-info global configuration command. To return to the default settings, use the no form of this command.

ip security eso-info source compartment-size default-bit
no ip security eso-info source compartment-size default-bit

Syntax Description

source

Hexadecimal or decimal value representing the extended IPSO source. This is an integer from 0 through 255.

compartment-size

Maximum number of bytes of compartment information allowed for a particular extended IPSO source. This is an integer from 1 through 16.

default-bit

Default bit value for any unsent compartment bits.

Default

Disabled

Command mode

Global configuration

Usage Guidelines

This command configures Extended Security Option (ESO) information, including Auxiliary Extended Security Option (AESO). Transmitted compartment info is padded to the size specified by the compartment-size argument.

Example

In the following example, system-wide defaults for source, compartment size, and the default bit value are set:

ip security eso-info 100 5 1
Related Commands

ip security eso-max
ip security eso-min

ip security eso-max

To specify the maximum sensitivity level for an interface, use the ip security eso-max interface configuration command. To return to the default, use the no form of this command.

ip security eso-max source compartment-bits
no ip security eso-max source compartment-bits

Syntax Description

source

Extended Security Option (ESO) source. This is an integer from 1 through 255.

compartment-bits

Compartment bits in hexadecimal.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command is used to specify the minimum sensitivity level for a particular interface. Before the per interface compartment information for a particular Network Level Extended Security Option (NLESO) source can be configured, the ip security eso-info global configuration command must be used to specify the default information.

On every incoming packet on the interface, these extended security options should be resent at the minimum level and should match the configured compartment bits. Every outgoing packet must have these ESOs.

On every packet transmitted or received on this interface, any NLESO sources present in the IP header should be bounded by the minimum sensitivity level and bounded by the maximum sensitivity level configured for the interface.

When transmitting locally generated traffic out this interface, or adding security information (with the ip security add command), the maximum compartment bit information can be used to construct the NLESO sources placed in the IP header.

A maximum of 16 NLESO sources can be configured per interface. Due to IP header length restrictions, a maximum of 9 of these NLESO sources appear in the IP header of a packet.

Example

In the following example, the specified ESO source is 240 and the compartment bits are specified as 500.

interface ethernet 0 ip security eso-max 240 500
Related Commands

ip security eso-info
ip security eso-min

ip security eso-min

To configure the minimum sensitivity for an interface, use the ip security eso-min interface configuration command. To return to the default, use the no form of this command.

ip security eso-min source compartment-bits
no ip security eso-min source compartment-bits

Syntax Description

source

Extended Security Option (ESO) source. This is an integer from 1 through 255.

compartment-bits

Compartment bits in hexadecimal.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command is used to specify the minimum sensitivity level for a particular interface. Before the per-interface compartment information for a particular Network Level Extended Security Option (NLESO) source can be configured, the ip security eso-info global configuration command must be used to specify the default information.

On every incoming packet on this interface, these extended security options should be resent at the minimum level and should match the configured compartment bits. Every outgoing packet must have these ESOs.

On every packet transmitted or received on this interface, any NLESO sources present in the IP header should be bounded by the minimum sensitivity level and bounded by the maximum sensitivity level configured for the interface.

When transmitting locally generated traffic out this interface, or adding security information (with the iip security add command), the maximum compartment bit information can be used to construct the NLESO sources placed in the IP header.

A maximum of 16 NLESO sources can be configured per interface. Due to IP header length restrictions, a maximum of 9 of these NLESO sources appear in the IP header of a packet.

Example

In the following example, the specified ESO source is 5 and the compartment bits are specified as 5.

interface ethernet 0 ip security eso-min 5 5
Related Commands

ip security eso-info
ip security eso-max

ip security extended-allowed

To accept packets on an interface that has an extended security option present, use the ip security extended-allowed interface configuration command. To restore the default, use the no form of this command.

ip security extended-allowed
no ip security extended-allowed


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

Packets containing extended security options are rejected.

Example

The following example allows interface Ethernet 0 to accept packets that have an extended security option present:

interface ethernet 0 ip security extended-allowed
Related Commands

ip security add
ip security dedicated
ip security first
ip security ignore-authorities
ip security implicit-labelling
ip security multilevel
ip security reserved-allowed
ip security strip

ip security first

To prioritize the presence of security options on a packet, use the ip security first interface configuration command. To disable this function, use the no form of this command.

ip security first
no ip security first


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

If a basic security option is present on an outgoing packet, but it is not the first IP option, then the packet is moved to the front of the options field when this interface configuration command is used.

Example

The following example ensures that, if a basic security option is present in the options field of a packet exiting interface Ethernet 0, the packet is moved to the front of the options field.

interface ethernet 0 ip security first
Related Commands

ip security add
ip security dedicated
ip security extended-allowed
ip security ignore-authorities
ip security implicit-labelling
ip security multilevel
ip security reserved-allowed
ip security strip

ip security ignore-authorities

To have the router ignore the authorities field of all incoming packets, use the ip security ignore-authorities interface configuration command. To disable this function, use the no form of this command.

ip security ignore-authorities
no ip security ignore-authorities


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

When the packet's authority field is ignored, the value used in place of this field is the authority value declared for the specified interface. IP security ignore-authorities can only be configured on interfaces with dedicated security levels.

Example

The following example causes interface Ethernet 0 to ignore the authorities field on all incoming packets:

interface ethernet 0 ip security ignore-authorities
Related Commands

ip security add
ip security dedicated
ip security extended-allowed
ip security first
ip security implicit-labelling
ip security multilevel
ip security reserved-allowed
ip security strip

ip security implicit-labelling

To force the router to accept packets on the interface, even if they do not include a security option, use the ip security implicit-labelling interface configuration command. To disable this function, use the no form of this command.

ip security implicit-labelling [level authority [authority...]]
no ip security implicit-labelling [level authority [authority...]]

Syntax Description

level

(Optional) Degree of sensitivity of information. If your interface has multilevel security set, you must specify this argument. The level keywords are listed in Table 17-1 (see the ip security dedicated interface configuration command).

authority

(Optional) Organization that defines the set of security levels that will be used in a network. If your interface has multilevel security set, you must specify this argument. You can specify more than one. The authority keywords are listed in Table 17-2 (see the ip security dedicated interface configuration command).

Default

Enabled, when the security level of the interface is "Unclassified Genser" (or unconfigured). Otherwise, the default is disabled.

Command Mode

Interface configuration

Usage Guidelines

If your interface has multilevel security set, you must use the expanded form of the command (with the optional arguments as noted in brackets) because the arguments are used to specify the precise level and authority to use when labeling the packet. If your interface has dedicated security set, the additional arguments are ignored.

Example

In the following example, an interface is set for security and will accept unlabeled packets:

ip security dedicated confidential genser ip security implicit-labelling
Related Commands

ip security add
ip security dedicated
ip security extended-allowed
ip security first
ip security ignore-authorities
ip security multilevel
ip security reserved-allowed
ip security strip

ip security multilevel

To set the range of classifications and authorities on an interface, use the ip security multilevel interface configuration command. To disable this function, use the no form of this command.

ip security multilevel level1 [authority1...] to level2 authority2 [authority2...]
no ip security multilevel


Syntax Description

level1

Degree of sensitivity of information. The classification level of incoming packets must be equal to or greater than this value for processing to occur. The level keywords are found in Table 17-1 (see the ip security dedicatedcommand).

authority1

(Optional) Organization that defines the set of security levels that will be used in a network. The authority bits must be a superset of this value. The authority keywords are listed in Table 17-2 (see the ip security dedicated command).

to

Separates the range of classifications and authorities.

level2

Degree of sensitivity of information. The classification level of incoming packets must be equal to or less than this value for processing to occur. The level keywords are found in Table 17-1 (see the ip security dedicated command).

authority2

Organization that defines the set of security levels that will be used in a network. The authority bits must be a proper subset of this value. The authority keywords are listed in Table 17-2 (see the ip security dedicated command).

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

All traffic entering or leaving the system must have a security option that falls within this range. Being within range requires that the following two conditions be met:

Example

The following example specifies levels Unclassified to Secret and NSA authority:

ip security multilevel unclassified to secret nsa
Related Commands

ip security add
ip security dedicated
ip security extended-allowed
ip security first
ip security ignore-authorities
ip security implicit-labelling
ip security reserved-allowed
ip security strip

ip security reserved-allowed

To treat as valid any packets that have Reserved1 through Reserved4 security levels, use the ip security reserved-allowed interface configuration command. To disable this feature, use the no form of this command.

ip security reserved-allowed
no ip security reserved-allowed


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

When you set multilevel security on an interface, and indicate, for example, that the highest range allowed is Confidential, and the lowest is Unclassified, the router neither allows nor operates on packets that have security levels of Reserved3 and Reserved2 because they are undefined.

If you use the IP Security Option (IPSO) to block transmission out of unclassified interfaces, and you use one of the Reserved security levels, you must enable this feature to preserve network security.

Example

The following example allows a security level of Reserved through Ethernet interface 0:

interface ethernet 0 ip security reserved-allowed
Related Commands

ip security add
ip security dedicated
ip security extended-allowed
ip security first
ip security ignore-authorities
ip security implicit-labelling
ip security multilevel
ip security strip

ip security strip

To remove any basic security option on outgoing packets on an interface, use the ip security strip interface configuration command. To disable this function, use the no form of this command.

ip security strip
no ip security strip


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This procedure is performed after all security tests in the router have been passed. This command is not allowed for multilevel interfaces.

Example

The following example removes any basic security options on outgoing packets on interface Ethernet 0:

interface ethernet 0 ip security strip
Related Commands

ip security add
ip security dedicated
ip security extended-allowed
ip security first
ip security ignore-authorities
ip security implicit-labelling
ip security multilevel
ip security reserved-allowed

ip source-route

To allow the router to handle IP datagrams with source routing header options, use the ip source-route global configuration command. To have the router discard any IP datagram containing a source-route option, use the no form of this command.

ip source-route
no ip source-route


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Global configuration

Example

The following example enables the handling of IP datagrams with source routing header options:

ip source-route
Related Commands

ping (privileged)
ping (user)

ip subnet-zero

To enable the use of subnet zero for interface addresses and routing updates, use the ip subnet-zero global configuration command. To restore the default, use the no form of this command.

ip subnet-zero
no ip subnet-zero


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

The ip subnet-zero command provides the ability to configure and route to subnet-zero subnets.

Subnetting with a subnet address of zero is discouraged because of the confusion inherent in having a network and a subnet with indistinguishable addresses.

Example

In the following example, subnet-zero is enabled for the router:

ip subnet-zero

ip tcp compression-connections

To specify the total number of header compression connections that can exist on an interface, uUse the ip tcp compression-connections interface configuration command. To restore the default, use the no form of this command.

ip tcp compression-connections number
no ip tcp compression-connections number

Syntax Description

number

Number of connections the cache supports. It can be a number from 3 through 256.

Default

16 connections

Command Mode

Interface configuration

Usage Guidelines

You should configure one connection for each TCP connection through the specified interface.

Each connection sets up a compression cache entry, so you are in effect specifying the maximum number of cache entries and the size of the cache. Too few cache entries for the specified interface can lead to degraded performance, while too many cache entries can lead to wasted memory.


Note Both ends of the serial connection must use the same number of cache entries.
Example

In the following example, the first serial interface is set for header compression with a maximum of ten cache entries:

interface serial 0 ip tcp header-compression ip tcp compression-connections 10
Related Commands

ip tcp header-compression
show ip tcp header-compression

ip tcp header-compression

To enable TCP header compression, use the ip tcp header-compression interface configuration command. To disable compression, use the no form of this command.

ip tcp header-compression [passive]
no ip tcp header-compression [passive]

Syntax Description

passive

(Optional) Compresses outgoing TCP packets only if incoming TCP packets on the same interface are compressed. If you do not specify the passive keyword, the router compresses all traffic.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

You can compress the headers of your TCP/IP packets in order to reduce the size of your packets. TCP header compression is supported on serial lines using HDLC or PPP encapsulation. You must enable compression on both ends of a serial connection. RFC 1144 specifies the compression process. Compressing the TCP header can speed up Telnet connections dramatically. In general, TCP header compression is advantageous when your traffic consists of many small packets, not for traffic that consists of large packets. Transaction processing (usually using terminals) tends to use small packets while file transfers use large packets. This feature only compresses the TCP header, so it has no effect on UDP packets or other protocol headers.

When compression is enabled, fast switching is disabled. This means that fast interfaces like T1 can overload the router. Consider your network's traffic characteristics before using this command.

Example

In the following example, the first serial interface is set for header compression with a maximum of ten cache entries:

interface serial 0 ip tcp header-compression ip tcp compression-connections 10
Related Commands

ip tcp compression-connections
show ip tcp header-compression

ip tcp path-mtu-discovery

To enable Path MTU Discovery for all new TCP connections from the router, use the ip tcp path-mtu-discovery interface configuration command. To disable the feature, use the no form of this command.

ip tcp path-mtu-discovery
no ip tcp path-mtu-discovery


Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

Path MTU Discovery is a method for maximizing the use of available bandwidth in the network between the end points of a TCP connection. It is described in RFC 1191. Existing connections are not affected when this feature is turned on or off.

Customers using TCP connections to move bulk data between systems on distinct subnets would benefit most by enabling this feature. This might include customers using RSRB with TCP encapsulation, STUN, X.25 Remote Switching (also known as XOT or X.25 over TCP), and some protocol translation configurations.

Example

In the following example, Path MTU Discovery is enabled:

ip tcp path-mtu-discovery

ip tcp synwait-time

To set a period of time the router waits while attempting to establish a TCP connection before it times out, use the ip tcp synwait-time global configuration command. To restore the default time, use the no form of this command.

ip tcp synwait-time seconds
no ip tcp synwait-time
seconds

Syntax Description

seconds

Time in seconds the router waits while attempting to establish a TCP connection. It can be an integer from 5 to 300 seconds. The default is 30 seconds.

Default

30 seconds

Command Mode

Global configuration

Usage Guidelines

In previous versions of router software, the system would wait a fixed 30 seconds when attempting to establish a TCP connection. If your network contains Public Switched Telephone Network Dial on Demand Routing (PSTN DDR), it is possible that the call setup time will exceed 30 seconds. This amount of time is not sufficient in networks that have dial-up asynchronous connections because it will affect your ability to Telnet over the link (from the router) if the link must be brought up. If you have this type of network, you might want to set this value to the UNIX value of 75.

Because this is a host parameter, it does not pertain to traffic going through the router, just for traffic originated at the router. Because UNIX has a fixed 75-second timeout, hosts are unlikely to see this problem.

Example

The following example configures the router to continue attempting to establish a TCP connection for 180 seconds:

ip tcp synwait-time 180

ip unnumbered

To enable IP processing on a serial interface without assigning an explicit IP address to the interface, use the ip unnumbered interface configuration command. To disable the IP processing on the interface, use the no form of this command.

ip unnumbered interface-name
no ip unnumbered interface-name

Syntax Description

interface-name

Name of another interface on which the router has an assigned IP address. It cannot be another unnumbered interface.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

Whenever the unnumbered interface generates a packet (for example, for a routing update), it uses the address of the specified interface as the source address of the IP packet. It also uses the address of the specified interface in determining which routing processes are sending updates over the unnumbered interface. Restrictions include the following:

The interface you specify by the interface-name argument must be enabled (listed as "up" in the show interfaces command display).

If you are configuring IS-IS across a serial line, you should configure the serial interfaces as unnumbered. This allows you to conform with RFC 1195, which states that IP addresses are not required on each interface.


Note Using an unnumbered serial line between different major networks (majornets) requires special care. If at each end of the link there are different majornets assigned to the interfaces you specified as unnumbered, then any routing protocol running across the serial line must not advertise subnet information.
Example

In the following example, the first serial interface is given Ethernet 0's address:

interface ethernet 0 ip address 131.108.6.6 255.255.255.0 interface serial 0 ip unnumbered ethernet 0

ip unreachables

To enable the generation of ICMP Unreachable messages, use the ip unreachables interface configuration command. To disable this function, use the no form of this command.

ip unreachables
no ip unreachables


Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Interface configuration

Usage Guidelines

If the router receives a nonbroadcast packet destined for itself that uses a protocol it does not recognize, it sends an ICMP Protocol Unreachable message to the source.

If the router receives a datagram that it cannot deliver to its ultimate destination because it knows of no route to the destination address, it replies to the originator of that datagram with an ICMP Host Unreachable message.

This command affects all kinds of ICMP unreachable messages.

Example

The following example enables the generation of ICMP Unreachable messages, as appropriate, on an interface:

interface ethernet 0 ip unreachables

ping (user)

To check host reachability and network connectivity, use the ping (IP packet internet groper function) user EXEC command.

ping [protocol] {host | address}

Syntax Description

protocol

(Optional) Protocol keyword. The default is IP.

host

Host name of system to ping.

address

IP address of system to ping.

Command Mode

EXEC

Usage Guidelines

The ping command sends ICMP Echo messages. If the router receives an ICMP Echo message, it sends an ICMP Echo Reply message to the source of the ICMP Echo message.

The user ping feature provides a basic ping facility for IP users who do not have system privileges. This feature allows the router to perform the simple default ping functionality for the IP protocol. Only the nonverbose form of the ping command is supported for user pings.

If the system cannot map an address for a host name, it will return an "%Unrecognized host or address" error message.

To abort a ping session, type the escape sequence (by default, Ctrl-^ X, which is done by simultaneously pressing the Ctrl, Shift, and 6 keys, letting go, then pressing the X key).

Table 17-3 describes the test characters that the ping facility sends.


Table 17-3: Ping Test Characters
Char Description

!

Each exclamation point indicates receipt of a reply.

.

Each period indicates the network server timed out while waiting for a reply.

U

Destination unreachable.

N

Network unreachable.

P

Protocol unreachable.

Q

Source quench.

M

Could not fragment.

?

Unknown packet type.

Sample Display Using an IP Host Name

The following display shows sample ping output when you ping a host named fred:

Router> ping fred Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.31.7.27, timeout is 2 seconds: !!!!! Success rate is 100 percent, round-trip min/avg/max = 1/3/4 ms
Sample Display Using the Broadcast Address

The following display shows sample ping output when you ping the broadcast address of 255.255.255.255:

Router> ping 255.255.255.255 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 255.255.255.255, timeout is 2 seconds: Reply to request 0 from 160.89.48.15 (4 ms) Reply to request 0 from 160.89.48.10 (4 ms) Reply to request 0 from 160.89.48.19 (4 ms) Reply to request 0 from 160.89.49.15 (4 ms) Reply to request 1 from 160.89.48.15 (4 ms) Reply to request 1 from 160.89.48.10 (4 ms) Reply to request 1 from 160.89.48.19 (4 ms) Reply to request 1 from 160.89.49.15 (4 ms) Reply to request 2 from 160.89.48.15 (4 ms) Reply to request 2 from 160.89.48.10 (4 ms) Reply to request 2 from 160.89.48.19 (4 ms) Reply to request 2 from 160.89.49.15 (4 ms) Reply to request 3 from 160.89.48.15 (4 ms) Reply to request 3 from 160.89.48.10 (4 ms) Reply to request 3 from 160.89.48.19 (4 ms) Reply to request 3 from 160.89.49.15 (4 ms) Reply to request 4 from 160.89.48.15 (4 ms) Reply to request 4 from 160.89.48.10 (4 ms) Reply to request 4 from 160.89.48.19 (4 ms) Reply to request 4 from 160.89.49.15 (4 ms)
Related Command

ping (privileged)

ping (privileged)

To check host reachability and network connectivity, use the ping (IP packet internet groper function) user EXEC command.

ping [protocol] {host | address}

Syntax Description

protocol

(Optional) Protocol keyword. The default is IP.

host

Host name of system to ping.

address

IP address of system to ping.

Command Mode

Privileged EXEC

Usage Guidelines

The ping command sends ICMP Echo messages. If the router receives an ICMP Echo message, it sends an ICMP Echo Reply message to the source of the ICMP Echo message.

You can use the IP ping command to diagnose serial line problems. By placing the local or remote CSU/DSU into loopback mode and pinging your own interface, you can isolate the problem to the router or leased line.

Multicast and broadcast pings are fully supported. When you ping the broadcast address of 255.255.255.255, the system will send out pings and print a list of all stations responding. You can also ping a local network to get a list of all systems that respond, as in the following example, where 128.111.3 is a local network:

ping 128.111.3.255

As a side-effect, you also can get a list of all multicast-capable hosts that are connected directly to the router from which you are pinging, as in the following example:

ping 224.0.0.1

To abort a ping session, type the escape sequence (by default, Ctrl-^ X, which is done by simultaneously pressing the Ctrl, Shift, and 6 keys, letting go, then pressing the X key).

Table 17-4 describes the test characters that the ping facility sends.


Table 17-4: Ping Test Characters
Char Description

!

Each exclamation point indicates receipt of a reply.

.

Each period indicates the network server timed out while waiting for a reply.

U

Destination unreachable.

N

Network unreachable.

P

Protocol unreachable.

Q

Source quench.

M

Could not fragment.

?

Unknown packet type.

You can use the extended command mode of the ping command to specify the supported Internet header options, as shown in the following sample display.

Sample Display Showing Extended Command Sequence

To enter ping extended command mode, enter yes at the extended commands prompt of the ping command. The following display shows a sample ping extended command sequence.

Router# ping Protocol [ip]: Target IP address: 192.31.7.27 Repeat count [5]: Datagram size [100]: Timeout in seconds [2]: Extended commands [n]: y Source address: 131.108.1.1 Type of service [0]: Set DF bit in IP header? [no]: Data pattern [0xABCD]: Loose, Strict, Record, Timestamp, Verbose[none]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.31.7.27, timeout is 2 seconds: !!!!! Success rate is 100 percent, round-trip min/avg/max = 1/3/4 ms

Table 17-5 describes significant fields shown in the display.


Table 17-5: IP Ping Internet Header Options Field Descriptions
Field Description

Protocol [ip]:

Default is IP.

Target IP address:

Prompts for the IP address or host name of the destination node you plan to ping.

Repeat count [5]:

Number of ping packets that will be sent to the destination address. Default: 5.

Datagram size [100]:

Size of the ping packet (in bytes). Default: 100 bytes.

Timeout in seconds [2]:

Timeout interval. Default: 2 (seconds).

Extended commands [n]:

Specifies whether or not a series of additional commands appears. Many of the following displays and tables show and describe these commands. Default: no.

Source address:

IP address that appears in the ping packet as the source address.

Type of service [0]:

Internet service quality selection. See RFC 791 for more information. Default: 0.

Set DF bit in IP header?

Don't Fragment. Specifies that if the packet encounters a node in its path that is configured for a smaller MTU than the packet's MTU, that the packet is to be dropped and an error message is to be sent to the router at the packet's source address. If performance problems are encountered on the network, a node configured for a small MTU could be a contributing factor. This feature can be used to determine the smallest MTU in the path. Default: no.

Data pattern [0xABCD]:

Sets 16-bit hexadecimal data pattern. Default: 0xABCD. Varying the data pattern in this field (to all ones or all zeros for example) can be useful when debugging data sensitivity problems on CSU/DSUs, or detecting cable-related problems such as cross talk.

Loose, Strict, Record, Timestamp, Verbose [none]:

Supported Internet header options. The router examines the header options to every packet that passes through it. If it finds a packet with an invalid option, the router sends an ICMP Parameter Problem message to the source of the packet and discards the packet. The Internet header options follow:

  • Loose

  • Strict

  • Record—See the following section for more information on this helpful option.

  • Timestamp

  • Verbose

Default: none. For more information on these header options, see RFC 791.

Sweep range of sizes [n]:

Allows you to vary the sizes of the echo packets being sent. This capability is useful for determining the minimum sizes of the MTUs configured on the nodes along the path to the destination address. Packet fragmentation contributing to performance problems can then be reduced.

!!!!!

Each exclamation point (!) indicates receipt of a reply. A period (.) indicates the network server timed out while waiting for a reply. Other characters may appear in the ping output display, depending on the protocol type.

Success rate is 100 percent

Percentage of packets successfully echoed back to the router. Anything less than 80 percent is usually considered problematic.

round-trip min/avg/max = 1/3/4 ms

Round-trip travel time intervals for the protocol echo packets, including minimum/average/maximum (in milliseconds).

Use the Record Route Option

Using the Record Route option to trace a path to a particular destination address. Be aware, however, that the trace EXEC command performs a similar function, but the latter does not have the nine-hop limitation.

Sample Display Showing the Record Route Option

The following display shows sample extended ping output when this option is specified:

Router# ping Protocol [ip]: Target IP address: fred Repeat count [5]: Datagram size [100]: Timeout in seconds [2]: Extended commands [n]: y Source address: Type of service [0]: Set DF bit in IP header? [no]: Data pattern [0xABCD]: Loose, Strict, Record, Timestamp, Verbose[none]: r Number of hops [ 9 ]: Loose, Strict, Record, Timestamp, Verbose[RV]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 131.108.1.115, timeout is 2 seconds: Packet has IP options: Total option bytes= 39, padded length=40 Record route: <*> 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0

The following display is a detail of the Echo packet section:

0 in 4 ms. Received packet has options Total option bytes= 40, padded length=40 Record route: 160.89.80.31 131.108.6.10 131.108.1.7 131.108.1.115 131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0 End of list 1 in 8 ms. Received packet has options Total option bytes= 40, padded length=40 Record route: 160.89.80.31 131.108.6.10 131.108.1.6 131.108.1.115 131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0 End of list 2 in 4 ms. Received packet has options Total option bytes= 40, padded length=40 Record route: 160.89.80.31 131.108.6.10 131.108.1.7 131.108.1.115 131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0 End of list 3 in 8 ms. Received packet has options Total option bytes= 40, padded length=40 Record route: 160.89.80.31 131.108.6.10 131.108.1.6 131.108.1.115 131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0 End of list 4 in 4 ms. Received packet has options Total option bytes= 40, padded length=40 Record route: 160.89.80.31 131.108.6.10 131.108.1.7 131.108.1.115 131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0 End of list Success rate is 100 percent, round-trip min/avg/max = 4/5/8 ms

Router#

In this display, five ping echo packets are sent to the destination address 131.108.1.115. The echo packet detail section includes specific information about each of these echo packets.

The lines of ping output that are unique when the Record Route option is specified are described as follows.

The following line of output allows you to specify the number of hops that will be recorded in the route. Range: 1 through 9. Default: 9.

Number of hops [ 9 ]:

The following line of output indicates that IP header options have been enabled on the outgoing echo packets and shows the number of option bytes and padded bytes in the headers of these packets.

Packet has IP options: Total option bytes= 39, padded length=40

The following lines of output indicate that the fields that will contain the IP addresses of the nodes in the routes have been zeroed out in the outgoing packets.

Record route: <*> 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0

The following lines of output display statistics for the first of the five echo packets sent. 0 is the number assigned to this packet to indicate that it is the first in the series. 4 ms indicates the round trip travel time for the packet.

0 in 4 ms. Received packet has options Total option bytes= 40, padded length=40 Record route: 160.89.80.31 131.108.6.10 131.108.1.7 131.108.1.115 131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0

The following line of output indicates that four nodes were included in the packet's route, including the router at source address 160.89.80.31, two intermediate nodes at addresses 131.108.6.10 and 131.108.1.7, and the destination node at address 131.108.1.115. The underlined address shows where the original route differs from the return route in the line that follows this line.

Record route: 160.89.80.31 131.108.6.10 131.108.1.7 131.108.1.115

The following line of output includes the addresses of the four nodes in the return path of the echo packet. The underlined address shows where the return route differs from the original route shown in the previous line of output.

131.108.1.115 131.108.6.7 160.89.80.240 160.89.80.31 <*> 0.0.0.0
Related Command

ping (user)

show access-lists

To display the contents of all current access lists, use the show access-lists privileged EXEC command.

show access-lists

Syntax Description

This command has no arguments or keywords.

Command Mode

Privileged EXEC

Sample Display

The following is sample output from the show access-lists command:

Router# show access-lists Standard IP access list 19      permit 131.108.19.0      deny 0.0.0.0, wildcard bits 255.255.255.255 Standard IP access list 49      permit 131.108.31.0, wildcard bits 0.0.0.255     permit 131.108.194.0, wildcard bits 0.0.0.255      permit 131.108.195.0, wildcard bits 0.0.0.255     permit 131.108.196.0, wildcard bits 0.0.0.255     permit 131.108.197.0, wildcard bits 0.0.0.255 Extended IP access list 101     permit tcp 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255 eq 23 Type code access list 201     permit 0x6001 0x0000 Type code access list 202     permit 0x6004 0x0000     deny 0x0000 0xFFFF

For information on how to configure access lists, refer to the "Configuring IP" chapter of the Router Products Configuration Guide.

Related Commands

access-list (extended)
access-list (standard)

show arp

To display the entries in the ARP table for the router, use the show arp privileged EXEC command.

show arp

Syntax Description

This command has no arguments or keywords.

Command Mode

Privileged EXEC

Sample Display

The following is sample output from the show arp command:

Router# show arp Protocol    Address           Age (min)    Hardware Addr     Type    Interface Internet    131.108.42.112    120          0000.a710.4baf    ARPA     Ethernet3 AppleTalk   4028.5            29           0000.0c01.0e56    SNAP     Ethernet2 Internet    131.108.42.114    105          0000.a710.859b    ARPA     Ethernet3 AppleTalk   4028.9            -            0000.0c02.a03c    SNAP     Ethernet2 Internet    131.108.42.121    42           0000.a710.68cd    ARPA     Ethernet3 Internet    131.108.36.9      -            0000.3080.6fd4    SNAP     TokenRing0 AppleTalk   4036.9            -            0000.3080.6fd4    SNAP     TokenRing0 Internet    131.108.33.9      -            0000.0c01.7bbd    SNAP     Fddi0

Table 17-6 describes significant fields shown in the first line of output in the display.


Table 17-6: Show ARP Field Descriptions
Field Description

Protocol

Indicates the type of network address this entry includes.

Address

Network address that is mapped to the MAC address in this entry.

Age (min)

Indicates the interval (in minutes) since this entry was entered in the table, rather than the interval since the entry was last used. (The timeout value is 4 hours.)

Hardware Addr

MAC address mapped to the network address in this entry.

Type

Indicates the encapsulation type the router is using for the network address in this entry. Possible values include:

  • ARPA

  • SNAP

  • ETLK (EtherTalk)

  • SMDS

Interface

Indicates the interface associated with this network address.

show dnsix

To display state information and the current configuration of the DNSIX audit writing module, use the show dnsix privileged EXEC command.

show dnsix

Syntax Description

This command has no arguments or keywords.

Command Mode

Privileged EXEC

Sample Display

The following is sample output from the show dnsix command:

Router# show dnsix Audit Trail Enabled with Source 128.105.2.5 State: PRIMARY Connected to 128.105.2.4 Primary 128.105.2.4 Transmit Count 1 DMDP retries 4 Authorization Redirection List: 128.105.2.4 Record count: 0 Packet Count: 0 Redirect Rcv: 0

show hosts

To display the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of host names and addresses, use the show hosts EXEC command.

show hosts

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show hosts command:

Router# show hosts Default domain is CISCO.COM Hame/address lookup uses domain service Hame servers are 255.255.255.255 Host               Flag         Age    Type        Address(es) SLAG.CISCO.COM     (temp, OK)   1      IP          131.108.4.10 CHAR.CISCO.COM     (temp, OK)   8      IP          192.31.7.50 CHAOS.CISCO.COM    (temp, OK)   8      IP          131.108.1.115 DIRT.CISCO.COM     (temp, EX)   8      IP          131.108.1.111 DUSTBIN.CISCO.COM  (temp, EX)   0      IP          131.108.1.27 DREGS.CISCO.COM    (temp, EX)   24     IP          131.108.1.30

Table 17-7 describes significant fields shown in the display.


Table 17-7: Show Hosts Field Descriptions
Field Description

Flag

A temporary entry is entered by a name server; the router removes the entry after 72 hours of inactivity.
A perm entry is entered by a configuration command and is not timed out. Entries marked OK are believed to be valid. Entries marked ?? are considered suspect and subject to revalidation. Entries marked EX are expired.

Age

Indicates the number of hours since the router last referred to the cache entry.

Type

Identifies the type of address, for example, IP, CLNS, or X.121. If you have used the ip hp-host global configuration command, the show hosts command will display these host names as type HP-IP.

Address(es)

Shows the address of the host. One host may have up to eight addresses.

Related Command

clear host

show ip access-list

To display the contents of all current IP access lists, use the show ip access-list EXEC command.

show ip access-list [access-list-number]

Syntax Description

access-list-number

(Optional) Number of the IP access list to display. This is a decimal number from 1 to 199.

Defaults

Displays all standard and extended IP access lists.

Command Mode

EXEC

Usage Guidelines

The show ip access-list command provides output identical to the show access-lists command, except that it is IP-specific and allows you to specify a particular access list.

Sample Display

The following is sample output from the show ip access-list command:

Router# show ip access-list Extended IP access list 101 deny udp any any eq ntp permit tcp any any permit udp any any eq tftp permit icmp any any permit udp any any eq domain

show ip accounting

To display the active accounting or checkpointed database or to display access-list violations, use the show ip accounting EXEC command.

show ip accounting [checkpoint] [output-packets | access-violations]

Syntax Description

checkpoint

(Optional) Indicates that the checkpointed database should be displayed.

output-packets

(Optional) Indicates that information pertaining to packets that passed access control and were successfully routed should be displayed. If neither the output-packets nor access-violations keyword is specified, output-packets is the default.

access-violations

(Optional) Indicates that information pertaining to packets that failed access lists and were not routed should be displayed. If neither the output-packets nor access-violations keyword is specified, output-packets is the default.

Defaults

If neither the output-packets nor access-violations keyword is specified, show ip accounting displays information pertaining to packets that passed access control and were successfully routed.

Command Mode

EXEC

Usage Guidelines

If you do not specify any keywords, the show ip accounting command displays information about the active accounting database.

To display IP access violations, you must give the access-violations keyword on the command. If you do not specify the keyword, the command defaults to displaying the number of packets that have passed access lists and were routed.

To use this command, you must first enable IP accounting on a per-interface basis.

Sample Display

Following is sample output from the show ip accounting command:

Router# show ip accounting Source Destination Packets Bytes 131.108.19.40 192.67.67.20 7 306 131.108.13.55 192.67.67.20 67 2749 131.108.2.50 192.12.33.51 17 1111 131.108.2.50 130.93.2.1 5 319 131.108.2.50 130.93.1.2 463 30991 131.108.19.40 130.93.2.1 4 262 131.108.19.40 130.93.1.2 28 2552 131.108.20.2 128.18.6.100 39 2184 131.108.13.55 130.93.1.2 35 3020 131.108.19.40 192.12.33.51 1986 95091 131.108.2.50 192.67.67.20 233 14908 131.108.13.28 192.67.67.53 390 24817 131.108.13.55 192.12.33.51 214669 9806659 131.108.13.111 128.18.6.23 27739 1126607 131.108.13.44 192.12.33.51 35412 1523980 192.31.7.21 130.93.1.2 11 824 131.108.13.28 192.12.33.2 21 1762 131.108.2.166 192.31.7.130 797 141054 131.108.3.11 192.67.67.53 4 246 192.31.7.21 192.12.33.51 15696 695635 192.31.7.24 192.67.67.20 21 916 131.108.13.111 128.18.10.1 16 1137

The following is sample output from the show ip accounting access-violations command. The output pertains to packets that failed access lists and were not routed:

Router# show ip accounting access-violations Source Destination Packets Bytes ACL 131.108.19.40 192.67.67.20 7 306 77 131.108.13.55 192.67.67.20 67 2749 185 131.108.2.50 192.12.33.51 17 1111 140
131.108.2.50 130.93.2.1 5 319 140
131.108.19.40 130.93.2.1 4 262 77 Accounting data age is 41

Table 17-8 describes the fields shown in the displays.


Table 17-8: Show IP Accounting (and Access-Violation) Field Descriptions
Field Description

Source

Source address of the packet.

Destination

Destination address of the packet.

Packets

Number of packets transmitted from the source address to the destination address.

With the access-violations keyword, the number of packets transmitted from the source address to the destination address that violated an access control list.

Bytes

Sum of the total number of bytes (IP header and data) of all IP packets transmitted from the source address to the destination address.

With the access-violations keyword, the total number of bytes transmitted from the source address to the destination address that violated an access-control list.

ACL

Number of the access list of the last packet transmitted from the source to the destination that failed an access list filter.

Related Commands

clear ip accounting
ip accounting
ip accounting-list
ip accounting-threshold
ip accounting-transits

show ip aliases

To display the router's IP addresses mapped to TCP ports (aliases) and SLIP addresses, which are treated similarly to aliases, use the show ip aliases EXEC command.

show ip aliases

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Usage Guidelines

To distinguish a SLIP address from a normal alias address, the command output uses the form SLIP TTY1 for the "port" number, where 1 is the auxiliary port.

Sample Display

The following is sample output from the show ip aliases command:

Router# show ip aliases IP Address Port 131.108.29.245 SLIP TTY1

The display lists the IP address and corresponding port number.

Related Command

A dagger (†) indicates that the command is documented in another chapter.

show line

show ip arp

To display the Address Resolution Protocol (ARP) cache, where SLIP addresses appear as permanent ARP table entries, use the show ip arp EXEC command.

show ip arp

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Usage Guidelines

ARP establishes correspondences between network addresses (an IP address, for example) and LAN hardware addresses (Ethernet addresses). A record of each correspondence is kept in a cache for a predetermined amount of time and then discarded.

Sample Display

The following is sample output from the show ip arp command:

Router# show ip arp Protocol Address Age (min) Hardware Addr Type Interface Internet 131.108.62.192 187 0800.2010.a3b6 ARPA Ethernet3 Internet 131.108.62.245 68 0800.200e.28f8 ARPA Ethernet3 Internet 131.108.1.140 139 0000.0c01.2812 ARPA Ethernet0 Internet 131.108.62.160 187 0800.200e.4dab ARPA Ethernet3 Internet 131.108.1.111 27 0800.2007.8866 ARPA Ethernet0 Internet 131.108.1.117 119 0000.0c00.f346 ARPA Ethernet0 Internet 131.108.1.115 28 0000.0c01.0509 ARPA Ethernet0 Internet 131.108.1.77 1 0800.200e.57ce ARPA Ethernet0 Internet 192.31.7.29 225 aa00.0400.0234 ARPA Ethernet2 Internet 192.31.7.17 118 2424.c01f.0711 ARPA Ethernet2 Internet 192.31.7.18 135 0000.0c01.2817 ARPA Ethernet2 Internet 192.31.7.21 119 2424.c01f.0715 ARPA Ethernet2 Internet 131.108.1.33 1 0800.2008.c52e ARPA Ethernet0 Internet 131.108.62.1 - 0000.0c00.750f ARPA Ethernet3 Internet 131.108.31.35 119 0800.2010.8c5b ARPA Ethernet7 Internet 131.108.62.7 14 0000.0c00.33ce ARPA Ethernet3 Internet 131.108.1.55 155 0800.200e.e443 ARPA Ethernet0

Table 17-9 describes significant fields shown in the display.


Table 17-9: Show IP ARP Field Displays
Field Description

Protocol

Protocol for network address in the Address field.

Address

The network address that corresponds to Hardware Addr.

Age (min)

Age, in minutes, of the cache entry.

Hardware Addr

LAN hardware address a MAC address that corresponds to network address.

Type

Type of encapsulation:

  • ARPA—Ethernet

  • SNAP—RFC 1042

  • SAP—IEEE 802.3

Interface

Interface to which this address mapping has been assigned.

show ip cache

To display the routing table cache used to fast switch IP traffic, use the show ip cache EXEC command.

show ip cache [prefix mask] [type number]

Syntax Description

prefix

(Optional) Display only the entries in the cache that match the prefix and mask combination.

mask

(Optional) Display only the entries in the cache that match the prefix and mask combination.

type

(Optional) Display only the entries in the cache that match the interface type and number combination.

number

(Optional) Display only the entries in the cache that match the interface type and number combination.

Command Mode

EXEC

Usage Guidelines

The show ip cache display shows MAC headers up to 92 bytes.

Sample Displays

The following is sample output from the show ip cache command:

Router# show ip cache IP routing cache version 4490, 141 entries, 20772 bytes, 0 hash overflows Minimum invalidation interval 2 seconds, maximum interval 5 seconds, quiet interval 3 seconds, threshold 0 requests Invalidation rate 0 in last second, 0 in last 3 seconds Last full cache invalidation occurred 0:06:31 ago Prefix/Length Age Interface MAC Header 131.108.1.1/32 0:01:09 Ethernet0/0 AA000400013400000C0357430800 131.108.1.7/32 0:04:32 Ethernet0/0 00000C01281200000C0357430800 131.108.1.12/32 0:02:53 Ethernet0/0 00000C029FD000000C0357430800 131.108.2.13/32 0:06:22 Fddi2/0 00000C05A3E000000C035753AAAA0300 00000800 131.108.2.160/32 0:06:12 Fddi2/0 00000C05A3E000000C035753AAAA0300 00000800 131.108.3.0/24 0:00:21 Ethernet1/2 00000C026BC600000C03574D0800 131.108.4.0/24 0:02:00 Ethernet1/2 00000C026BC600000C03574D0800 131.108.5.0/24 0:00:00 Ethernet1/2 00000C04520800000C03574D0800 131.108.10.15/32 0:05:17 Ethernet0/2 00000C025FF500000C0357450800 131.108.11.7/32 0:04:08 Ethernet1/2 00000C010E3A00000C03574D0800 131.108.11.12/32 0:05:10 Ethernet0/0 00000C01281200000C0357430800 131.108.11.57/32 0:06:29 Ethernet0/0 00000C01281200000C0357430800

Table 17-10 describes significant fields shown in the display.


Table 17-10: Show IP Cache Field Descriptions
Field Description

IP routing cache version

Version number of this table. This number is incremented any time the table is flushed.

entries

Number of valid entries.

bytes

Number of bytes of processor memory for valid entries.

hash overflows

Number of times autonomous switching cache overflowed.

Minimum invalidation interval

Minimum time delay between cache invalidation request and actual invalidation.

maximum interval

Maximum time delay between cache invalidation request and actual invalidation.

quiet interval

Length of time between cache flush requests before the cache will be flushed.

threshold n requests

Maximum number of requests that can occur while the cache is considered quiet.

Invalidation rate n in last m seconds

Number of cache invalidations during the last m second.s

0 in last 3 seconds

Number of cache invalidation requests during the last quiet interval.

Last full cache invalidation occurred nn:nn:nn ago

Time since last full cache invalidation was performed.

Prefix/Length

Network reachability information for cache entry.

Age

Age of cache entry.

Interface

Output interface type and number.

MAC Header

Layer 2 encapsulation information for cache entry.

The following is sample output from the show ip cache command with a prefix and mask specified:

Router# show ip cache 131.108.5.0 255.255.255.0 IP routing cache version 4490, 119 entries, 17464 bytes, 0 hash overflows Minimum invalidation interval 2 seconds, maximum interval 5 seconds, quiet interval 3 seconds, threshold 0 requests Invalidation rate 0 in last second, 0 in last 3 seconds Last full cache invalidation occurred 0:11:56 ago Prefix/Length Age Interface MAC Header 131.108.5.0/24 0:00:34 Ethernet1/2 00000C04520800000C03574D0800

The following is sample output from the show ip cache command with an interface specified:

Router# show ip cache e0/2 IP routing cache version 4490, 141 entries, 20772 bytes, 0 hash overflows Minimum invalidation interval 2 seconds, maximum interval 5 seconds, quiet interval 3 seconds, threshold 0 requests Invalidation rate 0 in last second, 0 in last 3 seconds Last full cache invalidation occurred 0:06:31 ago Prefix/Length Age Interface MAC Header 131.108.10.15/32 0:05:17 Ethernet0/2 00000C025FF500000C0357450800

show ip interface

To display the usability status of interfaces configured for IP, use the show ip interface EXEC command.

show ip interface [type number]

Syntax Description

type

(Optional) Interface type.

number

(Optional) Interface number.

Command Mode

EXEC

Usage Guidelines

A router automatically enters a directly connected route in the routing table if the interface is usable. A usable interface is one through which the router can send and receive packets. If the router determines that an interface is not usable, it removes the directly connected routing entry from the routing table. Removing the entry allows the router to use dynamic routing protocols to determine backup routes to the network (if any).

If the interface can provide two-way communication, the line protocol is marked "up." If the interface hardware is usable, the interface is marked "up."

If you specify an optional interface type, you will see only information on that specific interface.

If you specify no optional arguments, you will see information on all the interfaces.

Sample Display

The following is sample output from the show ip interface command:

Router# show ip interface Ethernet0 is up, line protocol is up Internet address is 192.195.78.24, subnet mask is 255.255.255.240 Broadcast address is 255.255.255.255 Address determined by non-volatile memory MTU is 1500 bytes Helper address is not set Secondary address 131.192.115.2, subnet mask 255.255.255.0   Directed broadcast forwarding is enabled Multicast groups joined: 224.0.0.1 224.0.0.2 Outgoing access list is not set Inbound access list is not set Proxy ARP is enabled Security level is default Split horizon is enabled ICMP redirects are always sent ICMP unreachables are always sent ICMP mask replies are never sent IP fast switching is enabled IP fast switching on the same interface is disabled IP SSE switching is disabled Router Discovery is disabled IP output packet accounting is disabled IP access violation accounting is disabled TCP/IP header compression is disabled Probe proxy name replies are disabled

Table 17-11 describes the fields shown in the display.


Table 17-11: Show IP Interface Field Descriptions
Field Description

Ethernet0 is up

If the interface hardware is usable, the interface is marked "up." For an interface to be usable, both the interface hardware and line protocol must be up.

line protocol is up

If the interface can provide two-way communication, the line protocol is marked "up." For an interface to be usable, both the interface hardware and line protocol must be up.

Broadcast address

Shows the broadcast address.

Address determined by ...

Indicates how the IP address of the interface was determined.

MTU

Shows the MTU value set on the interface.

Helper address

Shows a helper address if one has been set.

Secondary address

Shows a secondary address if one has been set.

Directed broadcast forwarding

Indicates whether directed broadcast forwarding is enabled.

Multicast groups joined

List which multicast groups this interface is a member of.

Outgoing access list

Indicates whether the interface has an outgoing access list set.

Inbound access list

Indicates whether the interface has an incoming access list set.

Proxy ARP

Indicates whether Proxy ARP is enabled for the interface.

Security level

Specifies the IPSO security level set for this interface.

ICMP redirects

Specifies whether redirects will be sent on this interface.

ICMP unreachables

Specifies whether unreachable messages will be sent on this interface.

ICMP mask replies

Specifies whether mask replies will be sent on this interface.

IP fast switching

Specifies whether fast switching has been enabled for this interface. It is generally enabled on serial interfaces, such as this one.

IP SSE switching

Specifies whether IP SSE switching is enabled.

Router Discovery

Specifies whether the discovery process has been enabled for this interface. It is generally disabled on serial interfaces.

IP output packet accounting

Specifies whether IP accounting is enabled for this interface and what the threshold (maximum number of entries) is.

TCP/IP header compression

Indicates whether compression is enabled or disabled.

Probe proxy name

Indicates whether HP Probe proxy name replies are generated.

show ip masks

To display the masks used for network addresses and the number of subnets using each mask, use the show ip masks EXEC command.

show ip masks address

Syntax Description

address

Network address for which a mask is required.

Command Mode

EXEC

Usage Guidelines

The show ip masks command is useful for debugging when variable-length subnet masks (VLSM) are used. It shows the number of masks associated with the network and the number of routes for each mask.

Sample Display

The following is sample output from the show ip masks command:

Router# show ip masks 131.108.0.0 Mask Reference count 255.255.255.255 2 255.255.255.0 3 255.255.0.0 1

show ip nhrp

To display the Next Hop Resolution Protocol (NHRP) cache, use the show ip nhrp EXEC command.

show ip nhrp [dynamic | static] [type number]

Syntax Description

dynamic

(Optional) Displays only the dynamic (learned) IP-to-NBMA address cache entries.

static

(Optional) Displays only the static IP-to-NBMA address entries in the cache (configured through the ip nhrp map command).

type

(Optional) Interface type about which to display the NHRP cache (for example, atm, tunnel).

number

(Optional) Interface number about which to display the NHRP cache.

Command Mode

EXEC

Sample Display

The following is sample output from the show ip nhrp command:

Router# show ip nhrp 10.0.0.2 255.255.255.255, ATM0/0 created 0:00:43 expire 1:59:16 Type: dynamic Flags: authoritative NBMA address: 11.1111.1111.1111.1111.1111.1111.1111.1111.1111.11 10.0.0.1 255.255.255.255, Tunnel0 created 0:10:03 expire 1:49:56 Type: static Flags: authoritative NBMA address: 11.1.1.2 Router#

Table 17-12 describes the fields in the display.


Table 17-12: Show IP NHRP Field Descriptions
Field Description

100.0.0.2 255.255.255.255

IP address and its network mask in the IP-to-NBMA address cache. The mask is currently always 255.255.255.255 because we do not support aggregation of NBMA information through NHRP.

ATM0/0 created 0:00:43

Interface type and number (in this case, ATM slot and port numbers) and how long ago it was created (hours:minutes:seconds).

expire 1:59:16

Time in which the positive and negative authoritative NBMA address will expire (hours:minutes:seconds). This value is based on the
ip nhrp holdtime command.

Type

Value can be one of the following:

  • dynamic—NBMA address was obtained from NHRP Request packet.

  • static—NBMA address was statically configured.

Flags

Value can be one of the following:

  • authoritative—Indicates that the NHRP information was obtained from the Next Hop Server or router that maintains the NBMA-to-IP addresss mapping for a particular destination.

  • implicit—Indicates that the information was learned not from an NHRP request generated from the local router, but from an NHRP packet being forwarded or from an NHRP request being received by the local router.

  • negative—For negative caching; indicates that the requested NBMA mapping could not be obtained.

NBMA address

Nonbroadcast, multiaccess address. The address format is appropriate for the type of network being used (for example, ATM, Ethernet, SMDS, multipoint tunnel).

Related Command

ip nhrp map

show ip nhrp traffic

To display Next Hop Resolution Protocol (NHRP) traffic statistics, use the show ip nhrp traffic EXEC command.

show ip nhrp traffic

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show ip nhrp traffic command:

Router# show ip nhrp traffic Tunnel0 request packets sent: 2 request packets received: 4 reply packets sent: 4 reply packets received: 2 register packets sent: 0 register packets received: 0 error packets sent: 0 error packets received: 0 Router#

Table 17-13 describes the fields in the display.


Table 17-13: Show IP NHRP Traffic Field Descriptions
Field Description

Tunnel 0

Interface type and number.

request packets sent

Number of NHRP Request packets originated from this station.

request packets received

Number of NHRP Request packets received by this station.

reply packets sent

Number of NHRP Reply packets originated from this station.

reply packets received

Number of NHRP Reply packets received by this station.

register packets sent

Number of NHRP Register packets originated from this station. Currently, our routers do not send Register packets, so this value is 0.

register packets received

Number of NHRP Register packets received by this station. Currently, our routers do not send Register packets, so this value is 0.

error packets sent

Number of NHRP Error packets originated by this station.

error packets received

Number of NHRP Error packets received by this station.

show ip redirects

To display the address of a default gateway (router) and the address of hosts for which a redirect has been received, use the show ip redirects EXEC command.

show ip redirects

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show ip redirects command:

Router# show ip redirects Default gateway is 160.89.80.29 Host Gateway Last Use Total Uses Interface 131.108.1.111 160.89.80.240 0:00 9 Ethernet0 128.95.1.4 160.89.80.240 0:00 4 Ethernet0 Router#
Related Command

ip redirects

show ip route

To display the entries in the routing table, use the show ip route EXEC command.

show ip route [address [mask]] | [protocol]

Syntax Description

address

(Optional) Address about which routing information should be displayed.

mask

(Optional) Argument for a subnet mask.

protocol

(Optional) Argument for a particular routing protocol, or static or connected.

Command Mode

EXEC

Sample Displays

The following is sample output from the show ip route command when entered when you do not specify an address:

Router# show ip route Codes: I - IGRP derived, R - RIP derived, O - OSPF derived C - connected, S - static, E - EGP derived, B - BGP derived * - candidate default route, IA - OSPF inter area route E1 - OSPF external type 1 route, E2 - OSPF external type 2 route Gateway of last resort is 131.119.254.240 to network 129.140.0.0 O E2 150.150.0.0 [160/5] via 131.119.254.6, 0:01:00, Ethernet2 E 192.67.131.0 [200/128] via 131.119.254.244, 0:02:22, Ethernet2 O E2 192.68.132.0 [160/5] via 131.119.254.6, 0:00:59, Ethernet2 O E2 130.130.0.0 [160/5] via 131.119.254.6, 0:00:59, Ethernet2 E 128.128.0.0 [200/128] via 131.119.254.244, 0:02:22, Ethernet2 E 129.129.0.0 [200/129] via 131.119.254.240, 0:02:22, Ethernet2 E 192.65.129.0 [200/128] via 131.119.254.244, 0:02:22, Ethernet2 E 131.131.0.0 [200/128] via 131.119.254.244, 0:02:22, Ethernet2 E 192.75.139.0 [200/129] via 131.119.254.240, 0:02:23, Ethernet2 E 192.16.208.0 [200/128] via 131.119.254.244, 0:02:22, Ethernet2 E 192.84.148.0 [200/129] via 131.119.254.240, 0:02:23, Ethernet2 E 192.31.223.0 [200/128] via 131.119.254.244, 0:02:22, Ethernet2 E 192.44.236.0 [200/129] via 131.119.254.240, 0:02:23, Ethernet2 E 140.141.0.0 [200/129] via 131.119.254.240, 0:02:22, Ethernet2 E 141.140.0.0 [200/129] via 131.119.254.240, 0:02:23, Ethernet2

The following is sample output that includes some IS-IS Level 2 routes learned:

Router# show ip route Codes: I - IGRP derived, R - RIP derived, O - OSPF derived C - connected, S - static, E - EGP derived, B - BGP derived i - IS-IS derived * - candidate default route, IA - OSPF inter area route E1 - OSPF external type 1 route, E2 - OSPF external type 2 route L1 - IS-IS level-1 route, L2 - IS-IS level-2 route Gateway of last resort is not set 160.89.0.0 is subnetted (mask is 255.255.255.0), 3 subnets C 160.89.64.0 255.255.255.0 is possibly down, routing via 0.0.0.0, Ethernet0 i L2 160.89.67.0 [115/20] via 160.89.64.240, 0:00:12, Ethernet0 i L2 160.89.66.0 [115/20] via 160.89.64.240, 0:00:12, Ethernet0

Table 17-14 describes the fields shown in the displays.


Table 17-14: Show IP Route Field Descriptions
Field Description

Codes

Codes defining how the route was learned and the type of route.

I

Route learned via IGRP.

R

Route learned from a RIP update.

O

Route learned from an OSPF update.

C

Directly connected network.

S

Statically defined route via the ip route command.

E

Route learned from EGP.

B

Route learned from BGP.

i

Router learned from IS-IS.

D

Route leaved via Enhanced IGRP.

*

Candidate default route. In the list of routes, the asterisk is the robin pointer. It indicates the last path used when a packet was forwarded. It applies only to non-fast-switched packets. The asterisk does not give an indication of which path will be used next when forwarding a non-fast-switched packet except when the paths are equal-cost paths. Paths can be equal cost only when runnign RIP.

IA

OSPF interarea route.

E1

OSPF external type 1 route.

E2

OSPF external type 2 route.

L1

IS-IS Level 1 route.

L2

IS-IS Level 2 route.

EX

External enhanced IGRP route.

150.150.0.0

Indicates the address of the remote network.

[160/5]

The first number in the brackets is the administrative distance of the information source; the second number is the metric for the route.

via 131.119.254.6

Specifies the address of the next router to the remote network.

0:01:00

Specifies the last time the route was updated in hours:minutes:seconds.

Ethernet 2

Specifies the interface through which the specified network can be reached.

The following is sample output from the show ip route command when you specify an address:

Router# show ip route 160.89.6.0 Routing entry for 160.89.6.0 (mask 255.255.255.0) Known via "connected", distance 0, metric 0 (connected) Tag 0 Routing Descriptor Blocks: * directly connected, via Ethernet1 Route metric is 0, traffic share count is 1

Table 17-15 describes the significant field shown in the display.


Table 17-15: Show IP Route Field Descriptions When You Specify an Address
Field Description

Mask

Network mask associated with the route.

Connected

Routing protocol name, or connected or static.

Distance

Administrative distance.

Metric

Route metric that was either configured or learned from the particular route.

Routing Descriptor Blocks

Up to 4: Indicates the IP address of the next hop or the interface to which the particular route is connected.

show ip route summary

To display summary information about entries in the routing table, use the show ip route summary EXEC command.

show ip route summary

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show ip route summary command:

Router# show ip route summary Route Source Networks Subnets Overhead Memory (bytes) connected 0 3 126 360 static 1 2 126 360 igrp 109 747 12 31878 91080 internal 3 360 Total 751 17 32130 92160 Router#

Table 17-16 describes the fields shown in the display:


Table 17-16: Show IP Route Summary Field Descriptions
Field Description

Route Source

Routing protocol name, or connected, static, or internal.
Internal—those routes that are in the primary routing table merely as markers to hold subnet routes. These routes are not owned by any routing protocol. There should be one of these internal routes for each subnetted network in the routing table.

Networks

The number of Class A, B, or C networks that are present in the routing table for each route source.

Subnets

The number of subnets that are present in the routing table for each route source, including host routes.

Overhead

Any additional memory involved in allocating the routes for the particular route source other than the memory specified under "Memory."

Memory

The number of bytes allocated to maintain all the routes for the particular route source.

Related Command

show ip route

show ip tcp header-compression

To display statistics about TCP header compression, use the show ip tcp header-compression EXEC command.

show ip tcp header-compression

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show ip tcp header-compression command:

Router# show ip tcp header-compression TCP/IP header compression statistics: Interface Serial1: (passive, compressing) Rcvd:     4060 total, 2891 compressed, 0 errors               0 dropped, 1 buffer copies, 0 buffer failures    Sent:     4284 total, 3224 compressed,              105295 bytes saved, 661973 bytes sent               1.15 efficiency improvement factor Connect:  16 slots, 1543 long searches, 2 misses, 99% hit ratio               Five minute miss rate 0 misses/sec, 0 max misses/sec

Table 17-17 describes significant fields shown in the display.


Table 17-17: Show IP TCP Header-Compression
Field Description

Rcvd:

 total

Total number of TCP packets received.

 compressed

Total number of TCP packets compressed.

 errors

Unknown packets.

 dropped

Number of packets dropped due to invalid compression.

 buffer copies

Number of packets that had to be copied into bigger buffers for decompression.

 buffer failures

Number of packets dropped due to a lack of buffers.

Sent:

 total

Total number of TCP packets sent.

 compressed

Total number of TCP packets compressed.

 bytes saved

Number of bytes reduced.

 bytes sent

Number of bytes sent.

 efficiency  improvement  factor

Improvement in line efficiency because of TCP header compression.

Connect:

 number of slots

Size of the cache.

 long searches

Indicates the number of times the software had to look to find a match.

 misses

Indicates the number of times a match could not be made. If your output shows a large miss rate, then the number of allowable simultaneous compression connections may be too small.

 hit ratio

Percentage of times the software found a match and was able to compress the header.

 Five minute miss rate

Calculates the miss rate over the previous 5 minutes for a longer-term (and more accurate) look at miss rate trends.

max misses/sec

Maximum value of the previous field.

Field Descriptions
Related Command

ip tcp header-compression

show ip traffic

To display statistics about IP traffic, use the show ip traffic EXEC command.

show ip traffic

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show ip traffic command:

Router# show ip traffic IP statistics:    Rcvd:  98 total, 98 local destination          0 format errors, 0 checksum errors, 0 bad hop count          0 unknown protocol, 0 not a gateway          0 security failures, 0 bad options    Frags: 0 reassembled, 0 timeouts, 0 too big          0 fragmented, 0 couldn't fragment    Bcast: 38 received, 52 sent    Sent: 44 generated, 0 forwarded          0 encapsulation failed, 0 no route ICMP statistics:    Rcvd:  0 checksum errors, 0 redirects, 0 unreachable, 0 echo          0 echo reply, 0 mask requests, 0 mask replies, 0 quench          0 parameter, 0 timestamp, 0 info request, 0 other    Sent:  0 redirects, 3 unreachable, 0 echo, 0 echo reply          0 mask requests, 0 mask replies, 0 quench, 0 timestamp          0 info reply, 0 time exceeded, 0 parameter problem UDP statistics:    Rcvd:  56 total, 0 checksum errors, 55 no port    Sent:  18 total, 0 forwarded broadcasts TCP statistics:   Rcvd:  0 total, 0 checksum errors, 0 no port    Sent:  0 total EGP statistics:    Rcvd:  0 total, 0 format errors, 0 checksum errors, 0 no listener   Sent:  0 total IGRP statistics:    Rcvd:  73 total, 0 checksum errors   Sent:  26 total HELLO statistics:    Rcvd:  0 total, 0 checksum errors    Sent:  0 total ARP statistics:    Rcvd:  20 requests, 17 replies, 0 reverse, 0 other    Sent:  0 requests, 9 replies (0 proxy), 0 reverse Probe statistics:    Rcvd:  6 address requests, 0 address replies 0 proxy name requests, 0 other    Sent:  0 address requests, 4 address replies (0 proxy)          0 proxy name replies

Table 17-18 describes significant fields shown in the display.


Table 17-18: Show IP Traffic Field Descriptions
Field Description

format errors

A gross error in the packet format, such as an impossible Internet header length.

bad hop count

Occurs when a packet is discarded because its time-to-live (TTL) field was decremented to zero.

encapsulation failed

Usually indicates that the router had no ARP request entry and therefore did not send a datagram.

no route

Counted when the router discards a datagram it did not know how to route.

proxy name reply

Counted when the router sends an ARP or Probe Reply on behalf of another host. The display shows the number of probe proxy requests that have been received and the number of responses that have been sent.

show sse summary

To display a summary of Silicon Switch Processor (SSP) statistics, use the show sse summary EXEC command.

show sse summary

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show sse summary command:

Router# show sse summary SSE utilization statistics Program words Rewrite bytes Internal nodes Depth Overhead 499 1 8 IP 0 0 0 0 IPX 0 0 0 0 SRB 0 0 0 0 CLNP 0 0 0 0 IP access lists 0 0 0 Total used 499 1 8 Total free 65037 262143 Total available 65536 262144 Free program memory [499..65535] Free rewrite memory [1..262143] Internals 75032 internal nodes allocated, 75024 freed SSE manager process enabled, microcode enabled, 0 hangs Longest cache computation 4ms, longest quantum 160ms at 0x53AC8

show standby

To display Hot Standby Router Protocol information, use the show standby EXEC command.

show standby

Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Sample Display

The following is sample output from the show standby command:

Router# show standby Ethernet0 - Group 0 Local state is Active, priority 100, may preempt Hellotime 3 holdtime 10 Next hello sent in 0:00:00 Hot standby IP address is 198.92.72.29 configured Active router is local Standby router is 198.92.72.21 expires in 0:00:07   Tracking interface states for 2 interfaces, 2 up:     Up    Ethernet0     Up    Serial0

Table 17-19 describes the fields in the display.


Table 17-19: Show Standby Field Descriptions
Field Description

Ethernet0 - Group 0

Interface type and number and Hot Standby group number for the interface.

Local state is ...

State of local router; can be one of the following:

  • Active—Current Hot Standby router

  • Standby—Router next in line to be the Hot Standby router

priority

Priority value of the router based on the standby priority command.

may preempt

Indicates that the router will attempt to assume control as the active router if its priority is greater than the current active router.

Hellotime

Time between hello packets in seconds, based on the standby timers command.

holdtime

Time (in seconds) before other routers declare the active or standby router to be down, based on the standby timers command.

Next hello sent in ...

Time in which the router will send the next hello packet (in hours:minutes:seconds).

Hot Standby IP address is ... configured

IP address of the current Hot Standby router. The word "configured" indicates that this address is known through the standby ip command. Otherwise, the address was learned dynamically through HSRP hello packets from other routers that do have the HSRP IP address configured.

Active router is ...

Value can be "local" or an IP address. Address of the current active Hot Standby router.

Standby router is ...

Value can be "local" or an IP address. Address of the "standby" router (the router that is next in line to be the Hot Standby router).

expires in

Time (in hours:minutes:seconds) in which the standby router will no longer be the standby router if the local router receives no hello packets from it.

Tracking interface states for ...

List of interfaces that are being tracked and their corresponding states. Based on the standby track command.

standby authentication

To configure an authentication string for the Hot Standby Router Protocol, use the standby authentication interface configuration command. To delete an authentication string, use the no form of this command.

standby [group-number] authentication string
no standby [group-number] authentication string

Syntax Description

group-number

(Optional) Group number on the interface to which this authentication string applies.

string

Authentication string. It can be up to eight characters in length. The default string is cisco.

Defaults

group-number: 0
string: cisco

Command Mode

Interface configuration

Usage Guidelines

The authentication string is transmitted unencrypted in all Hot Standby Router Protocol messages. The same authentication string must be configured on all routers on a cable to ensure interoperation. Authentication mismatch prevents a router from learning the designated Hot Standby IP address and the Hot Standby timer values from other routers configured with the Hot Standby Router Protocol. Authentication mismatch does not prevent protocol events such as one router taking over as the designated router.

When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.

Example

In the following example, "word" is configured as the authentication string required to allow Hot Standby routers in group 1 to interoperate.

interface ethernet 0 standby 1 authentication word

standby ip

To activate the Hot Standby Router Protocol, use the standby ip interface configuration command. To disable the Hot Standby Router Protocol, use the no form of this command.

standby [group-number] ip [ip-address]
no standby [group-number] ip [ip-address]

Syntax Description

group-number

(Optional) Group number on the interface for which the Hot Standby Router Protocol is being activated.

ip-address

(Optional) IP address of the Hot Standby Router interface.

Defaults

group-number: 0
Hot Standby Router Protocol is disabled.

Command Mode

Interface configuration

Usage Guidelines

The standby ip command activates the Hot Standby Router Protocol on the configured interface. If an IP address is specified, that address is used as the designated address for the Hot Standby group. If no IP address is specified, the designated address is learned through the standby function. For the Hot Standby Router Protocol to elect a designated router, at least one router on the cable must have been configured with, or learned, the designated address. Configuring the designated address on the active router always overrides a designated address that is currently in use.

When the standby ip command is enabled on an interface, the handling of proxy ARP requests is changed (unless proxy ARP was disabled). If the interface's Hot Standby state is active, proxy ARP requests are answered using the Hot Standby group's MAC address. If the interface is in a different state, proxy ARP responses are suppressed.

When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.

Example

In the following example, the Hot Standby protocol is enabled for group 1 on Ethernet interface 0. The IP address used by the Hot Standby group will be learned using the Hot Standby Router Protocol.

interface ethernet 0 standby 1 ip

standby preempt

To indicate that, when the local router has a Hot Standby priority higher than the current active router, the local router should attempt to assume control as the active router, use the standby preempt interface configuration command. To have the local router assume control as the active router only if it receives information indicating that there is no router currently in the active state (acting as the designated router), use the no form of this command.

standby [group-number] preempt
no standby
[group-number] preempt

Syntax Description

group-number

(Optional) Group number on the interface for which the Hot Standby preemptive feature is being activated.

Defaults

group-number: 0
The local router assumes control as the active router only if it receives information indicating that there is no router currently in the active state.

Command Mode

Interface configuration

Usage Guidelines

When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.

Example

In the following example, group 1 on Ethernet interface 0 is configured to preempt the current leader if the interface has a higher priority:

interface ethernet 0 standby 1 preempt
Related Commands

standby priority
standby track

standby priority

To prioritize a potential Hot Standby router, use the standby priority interface configuration command. To restore the priority to the default, use the no form of this command.

standby [group-number] priority priority-number
no standby [group-number] priority priority-number

Syntax Description

group-number

(Optional) Group number on the interface to which the priority number applies.

priority-number

Priority value. It is an integer from 0 through 255. The default is 100.

Defaults

group-number: 0
priority-number: 100

Command Mode

Interface configuration

Usage Guidelines

The assigned priority is used to help select the active and standby routers. Assuming preemption is enabled, the router with the highest priority becomes the designated active router. In case of ties, the primary IP addresses are compared, and the higher IP address has priority.

Note that the router's priority can change dynamically if an interface is configured with the standby track command and another interface on the router goes down.

When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.

Example

In the following example, group number 1 on Ethernet interface 0 is assigned with priority 150:

interface ethernet 0 standby 1 priority 150
Related Commands

standby preempt
standby track

standby timers

To configure the time between hellos and the time before other routers declare the active Hot Standby or standby router to be down, use the standby timers interface configuration command. To restore the timers to their default values, use the no form of this command.

standby [group-number] timers hellotime holdtime
no standby [group-number] timers hellotime holdtime

Syntax Description

group-number

(Optional) Group number on the interface to which the timers apply. The default is 0.

hellotime

Hello interval in seconds. This is an integer from 1 through 255. The default is 1 second.

holdtime

Time in seconds before the active or standby router is declared to be down. This is an integer from 1 through 255. The default is 3 seconds.

Defaults

group-number: 0
hellotime: 1 second
holdtime: 3 seconds

Command Mode

Interface configuration

Usage Guidelines

The standby timers command configures the time between standby hellos and the time before other routers declare the active or standby router to be down. Routers on which timer values are not configured can learn timer values from the active or standby router. The timers configured on the active router always override any other timer settings. All routers in a Hot Standby group should use the same timer values. Normally, holdtime is greater than or equal to 3 times hellotime (holdtime >= 3 x hellotime).

When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.

Example

In the following example, for group number 1 on Ethernet interface 0, the time between hello packets is set to 5 seconds, and the time after which a router is considered to be down is set to 15 seconds:

interface ethernet 0 standby 1 ip standby 1 timers 5 15

standby track

To configure an interface so that the router's Hot Standby priority changes based on the availability of other interfaces, use the standby track interface configuration command. To remove the tracking, use the no form of this command.

standby [group-number] track type number [interface-priority]
no standby [group-number] track type number [interface-priority]

Syntax Description

group-number

(Optional) Group number on the interface to which the tracking applies.

type

Interface type (combined with interface number) that will be tracked.

number

Interface number (combined with interface type) that will be tracked.

interface-priority

(Optional) Amount by which the Hot Standby priority for the router is decremented (or incremented) when the interface goes down (or comes back up). The default value is 10.

Defaults

group-number: 0
interface-priority: 10

Command Mode

Interface configuration

Usage Guidelines

This command ties the router's Hot Standby priority to the availability of its interfaces. It is useful for tracking interfaces that are not configured for the Hot Standby Router Protocol.

When a tracked interface goes down, the Hot Standby priority of the router decreases by 10. If an interface is not tracked, its state changes do not affect the Hot Standby priority of the router. For each interface configured for Hot Standby, you can configure a separate list of interfaces to be tracked.

The optional argument interface-priority specifies how much to decrement the router's Hot Standby priority by when a tracked interface goes down. When the tracked interface comes back up, the router's priority is incremented by the same amount.

When multiple tracked interfaces are down and interface-priority values have been configured, these configured priority decrements are cumulative. If tracked interfaces are down, but none of them were configured with priority decrements, the default decrement is 10 and it is noncumulative.

When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.

Example

In the following example, Ethernet interface 1 tracks Ethernet interface 0 and serial interface 0. If one or both of these two interfaces go down, the Hot Standby priority of the router decreases by 10. Because the default Hot Standby priority is 100, the priority becomes 90 when one or both of the tracked interfaces go down.

interface ethernet 1 ip address 198.92.72.37 255.255.255.240 no ip redirects standby track ethernet 0 standby track serial 0 standby preempt standby ip 198.92.72.46
Related Commands

standby preempt
standby priority

term ip netmask-format

To specify the format in which netmasks are displayed in show command output, use the term ip netmask-format EXEC command. To restore the default display format, use the no form of this command.

term ip netmask-format {bitcount | decimal | hexadecimal}
term no ip netmask-format [bitcount | decimal | hexadecimal]

Syntax Description

bitcount

Addresses are followed by a slash and the total number of bits in the netmask. For example, 131.108.11.55/24 indicates that the netmask is 24 bits.

decimal

Netmasks are displayed in dotted decimal notation (for example, 255.255.255.0).

hexadecimal

Netmasks are displayed in hexadecimal format, as indicated by the leading 0X (for example, 0XFFFFFF00).

Default

Netmasks are displayed in dotted decimal format.

Command Mode

EXEC

Usage Guidelines

IP uses a 32-bit mask that indicates which address bits belong to the network and subnetwork fields and which bits belong to the host field. This is called a netmask. By default, show commands display an IP address and then its netmask in dotted decimal notation. For example, a subnet would be displayed as 131.108.11.55 255.255.255.0.

However, you can specify that the display of the network mask appear in hexadecimal format or bit count format instead. The hexadecimal format is commonly used on UNIX systems. The above example would be displayed as 131.108.11.55 0XFFFFFF00.

The bitcount format for displaying network masks is to append a slash (/) and the total number of bits in the netmask to the address itself. The above example would be displayed as 131.108.11.55/24.

Example

The following example specifies that network masks for the session be displayed in bitcount notation in the output of show commands:

term ip netmask-format bitcount

trace (user)

To discover the routes the router's packets follow when traveling to their destination, use the trace user EXEC command.

trace ip destination

Syntax Description

destination

Destination address or host name on the command line. The default parameters for the appropriate protocol are assumed and the tracing action begins.

Command Mode

EXEC

Usage Guidelines

The trace command works by taking advantage of the error messages generated by routers when a datagram exceeds its time-to-live (TTL) value.

The trace command starts by sending probe datagrams with a TTL value of one. This causes the first router to discard the probe datagram and send back an error message. The trace command sends several probes at each TTL level and displays the round-trip time for each.

The trace command sends out one probe at a time. Each outgoing packet may result in one or two error messages. A time exceeded error message indicates that an intermediate router has seen and discarded the probe. A destination unreachable error message indicates that the destination node has received the probe and discarded it because it could not deliver the packet. If the timer goes off before a response comes in, trace prints an asterisk (*).

The trace command terminates when the destination responds, when the maximum TTL is exceeded, or when the user interrupts the trace with the escape sequence. By default, to invoke the escape sequence, press Ctrl-^ X, which is done by simultaneously pressing the Ctrl, Shift, and 6 keys, letting go, then pressing the X key.

Common Trace Problems

Due to bugs in the IP implementation of various hosts and routers, the IP trace command may behave in odd ways.

Not all destinations will respond correctly to a probe message by sending back an ICMP port unreachable message. A long sequence of TTL levels with only asterisks, terminating only when the maximum TTL has been reached, may indicate this problem.

There is a known problem with the way some hosts handle an ICMP TTL exceeded message. Some hosts generate an ICMP message but they reuse the TTL of the incoming packet. Since this is zero, the ICMP packets do not make it back. When you trace the path to such a host, you may see a set of TTL values with asterisks (*). Eventually the TTL gets high enough that the ICMP message can get back. For example, if the host is six hops away, trace will time out on responses 6 through 11.

Sample Display Showing Trace IP Routes

The following display shows sample IP trace output when a destination host name has been specified:

Router# trace ip ABA.NYC.mil Type escape sequence to abort. Tracing the route to ABA.NYC.mil (26.0.0.73)    1 DEBRIS.CISCO.COM (131.108.1.6) 1000 msec 8 msec 4 msec    2 BARRNET-GW.CISCO.COM (131.108.16.2) 8 msec 8 msec 8 msec    3 EXTERNAL-A-GATEWAY.STANFORD.EDU (192.42.110.225) 8 msec 4 msec 4 msec    4 BB2.SU.BARRNET.NET (131.119.254.6) 8 msec 8 msec 8 msec    5 SU.ARC.BARRNET.NET (131.119.3.8) 12 msec 12 msec 8 msec    6 MOFFETT-FLD-MB.in.MIL (192.52.195.1) 216 msec 120 msec 132 msec    7 ABA.NYC.mil (26.0.0.73) 412 msec 628 msec 664 msec

Table 17-20 describes the fields shown in the display.


Table 17-20: Trace Field Descriptions
Field Description

1

Indicates the sequence number of the router in the path to the host.

DEBRIS.CISCO.COM

Host name of this router.

131.108.1.61

Internet address of this router.

1000 msec 8 msec 4 msec

Round-trip time for each of the three probes that are sent.

Table 17-21 describes the characters that can appear in trace output.


Table 17-21: IP Trace Text Characters
Char Description

nn msec

For each node, the round-trip time in milliseconds for the specified number of probes.

*

The probe timed out.

?

Unknown packet type.

Q

Source quench.

P

Protocol unreachable.

N

Network unreachable.

U

Port unreachable.

H

Host unreachable.

Related Command

trace (privileged)

trace (privileged)

To discover the routes the router's packets follow when traveling to their destination, use the trace privileged EXEC command.

trace [destination]

Syntax Description

destination

(Optional) Destination address or host name on the command line. The default parameters for the appropriate protocol are assumed and the tracing action begins.

Command Mode

Privileged EXEC

Usage Guidelines

The trace command works by taking advantage of the error messages generated by routers when a datagram exceeds its time-to-live (TTL) value.

The trace command starts by sending probe datagrams with a TTL value of one. This causes the first router to discard the probe datagram and send back an error message. The trace command sends several probes at each TTL level and displays the round-trip time for each.

The trace command sends out one probe at a time. Each outgoing packet may result in one or two error messages. A time exceeded error message indicates that an intermediate router has seen and discarded the probe. A destination unreachable error message indicates that the destination node has received the probe and discarded it because it could not deliver the packet. If the timer goes off before a response comes in, trace prints an asterisk (*).

The trace command terminates when the destination responds, when the maximum TTL is exceeded, or when the user interrupts the trace with the escape sequence. By default, to invoke the escape sequence, press Ctrl-^ X, which is done by simultaneously pressing the Ctrl, Shift, and 6 keys, letting go, then pressing the X key.

To use nondefault parameters and invoke an extended trace test, enter the command without a destination argument. You will be stepped through a dialog to select the desired parameters.

Common Trace Problems

Due to bugs in the IP implementation of various hosts and routers, the IP trace command may behave in odd ways.

Not all destinations will respond correctly to a probe message by sending back an ICMP port unreachable message. A long sequence of TTL levels with only asterisks, terminating only when the maximum TTL has been reached, may indicate this problem.

There is a known problem with the way some hosts handle an ICMP TTL exceeded message. Some hosts generate an ICMP message but they reuse the TTL of the incoming packet. Since this is zero, the ICMP packets do not make it back. When you trace the path to such a host, you may see a set of TTL values with asterisks (*). Eventually the TTL gets high enough that the ICMP message can get back. For example, if the host is six hops away, trace will time out on responses 6 through 11.

Sample Display Showing Trace IP Routes

The following display shows sample IP trace output when a destination host name has been specified:

Router# trace ABA.NYC.mil Type escape sequence to abort. Tracing the route to ABA.NYC.mil (26.0.0.73)    1 DEBRIS.CISCO.COM (131.108.1.6) 1000 msec 8 msec 4 msec    2 BARRNET-GW.CISCO.COM (131.108.16.2) 8 msec 8 msec 8 msec    3 EXTERNAL-A-GATEWAY.STANFORD.EDU (192.42.110.225) 8 msec 4 msec 4 msec    4 BB2.SU.BARRNET.NET (131.119.254.6) 8 msec 8 msec 8 msec    5 SU.ARC.BARRNET.NET (131.119.3.8) 12 msec 12 msec 8 msec    6 MOFFETT-FLD-MB.in.MIL (192.52.195.1) 216 msec 120 msec 132 msec    7 ABA.NYC.mil (26.0.0.73) 412 msec 628 msec 664 msec

Table 17-22 describes the fields shown in the display.


Table 17-22: Trace Field Descriptions
Field Description

1

Indicates the sequence number of the router in the path to the host.

DEBRIS.CISCO.COM

Host name of this router.

131.108.1.61

Internet address of this router.

1000 msec 8 msec 4 msec

Round-trip time for each of the three probes that are sent.

Sample Display Showing Extended IP Trace Dialog

The following display shows a sample trace session involving the extended dialog of the trace command:

Router# trace Protocol [ip]: Target IP address: mit.edu Source address: Numeric display [n]: Timeout in seconds [3]: Probe count [3]: Minimum Time to Live [1]: Maximum Time to Live [30]: Port Number [33434]: Loose, Strict, Record, Timestamp, Verbose[none]: Type escape sequence to abort. Tracing the route to MIT.EDU (18.72.2.1) 1 ICM-DC-2-V1.ICP.NET (192.108.209.17) 72 msec 72 msec 88 msec 2 ICM-FIX-E-H0-T3.ICP.NET (192.157.65.122) 80 msec 128 msec 80 msec 3 192.203.229.246 540 msec 88 msec 84 msec 4 T3-2.WASHINGTON-DC-CNSS58.T3.ANS.NET (140.222.58.3) 84 msec 116 msec 88 msec 5 T3-3.WASHINGTON-DC-CNSS56.T3.ANS.NET (140.222.56.4) 80 msec 132 msec 88 msec 6 T3-0.NEW-YORK-CNSS32.T3.ANS.NET (140.222.32.1) 92 msec 132 msec 88 msec 7 T3-0.HARTFORD-CNSS48.T3.ANS.NET (140.222.48.1) 88 msec 88 msec 88 msec 8 T3-0.HARTFORD-CNSS49.T3.ANS.NET (140.222.49.1) 96 msec 104 msec 96 msec 9 T3-0.ENSS134.T3.ANS.NET (140.222.134.1) 92 msec 128 msec 92 msec 10 W91-CISCO-EXTERNAL-FDDI.MIT.EDU (192.233.33.1) 92 msec 92 msec 112 msec 11 E40-RTR-FDDI.MIT.EDU (18.168.0.2) 92 msec 120 msec 96 msec 12 MIT.EDU (18.72.2.1) 96 msec 92 msec 96 msec  

Table 17-23 describes the fields that are unique to the extended trace sequence, as shown in the display.


Table 17-23: Trace Field Descriptions
Field Description

Target IP address

You must enter a host name or an IP address. There is no default.

Source address

One of the interface addresses of the router to use as a source address for the probes. The router will normally pick what it feels is the best source address to use.

Numeric display

The default is to have both a symbolic and numeric display; however, you can suppress the symbolic display.

Timeout in seconds

The number of seconds to wait for a response to a probe packet. The default is 3 seconds.

Probe count

The number of probes to be sent at each TTL level. The default count is 3.

Minimum Time to Live [1]

The TTL value for the first probes. The default is 1, but it can be set to a higher value to suppress the display of known hops.

Maximum Time to Live [30]

The largest TTL value that can be used. The default is 30. The trace command terminates when the destination is reached or when this value is reached.

Port Number

The destination port used by the UDP probe messages. The default is 33434.

Loose, Strict, Record, Timestamp, Verbose

IP header options. You may specify any combination. The trace command issues prompts for the required fields. Note that trace will place the requested options in each probe; however, there is no guarantee that all routers (or end nodes) will process the options.

Loose Source Routing

Allows you to specify a list of nodes that must be traversed when going to the destination.

Strict Source Routing

Allows you to specify a list of nodes that must be the only nodes traversed when going to the destination.

Record

Allows you to specify the number of hops to leave room for.

Timestamp

Allows you to specify the number of time stamps to leave room for.

Verbose

If you select any option, the verbose mode is automatically selected and trace prints the contents of the option field in any incoming packets. You can prevent verbose mode by selecting it again, toggling its current setting.

Table 17-24 describes the characters that can appear in trace output.


Table 17-24: IP Trace Text Characters
Char Description

nn msec

For each node, the round-trip time in milliseconds for the specified number of probes.

*

The probe timed out.

?

Unknown packet type.

Q

Source quench.

P

Protocol unreachable.

N

Network unreachable.

U

Port unreachable.

H

Host unreachable.

Related Command

trace (user)

transmit-interface

To assign a transmit interface to a receive-only interface, use the transmit-interface interface configuration command. To return to normal duplex Ethernet interfaces, use the no form of this command.

transmit-interface type number
no transmit-interface

Syntax Description

type

Transmit interface type to be linked with the (current) receive-only interface.

number

Transmit interface number to be linked with the (current) receive-only interface.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

Receive-only interfaces are used commonly with microwave Ethernet links.

Example

The following example specifies Ethernet interface 0 as a simplex Ethernet interface:

interface ethernet 1 ip address 128.9.1.2 transmit-interface ethernet 0

tunnel mode

To set the encapsulation mode for the tunnel interface, use the tunnel mode interface configuration command. To set to the default, use the no form of this command.

tunnel mode {aurp | cayman | dvmrp | eon | gre ip [multipoint] | nos}
no tunnel mode

Syntax Description

aurp

AppleTalk Update Routing Protocol (AURP).

cayman

Cayman TunnelTalk AppleTalk encapsulation.

dvmrp

Distance Vector Multicast Routing Protocol.

eon

EON compatible CLNS tunnel.

gre ip

Generic route encapsulation (GRE) protocol over IP.

multipoint

(Optional) Enables a GRE tunnel to be used in a multipoint fashion. Can be used with the gre ip keyword only, and requires the use of the tunnel key command.

nos

KA9Q/NOS compatible IP over IP.

Default

GRE tunneling

Command Mode

Interface configuration

Usage Guidelines

You cannot have two tunnels using the same encapsulation mode with exactly the same source and destination address. The workaround is to create a loopback interface and source packets off of the loopback interface.

Cayman tunneling implements tunneling as designed by Cayman Systems. This enables our routers to interoperate with Cayman GatorBoxes. With Cayman tunneling, you can establish tunnels between two routers or between our router and a GatorBox. When using Cayman tunneling, you must not configure the tunnel with an AppleTalk network address. This means that there is no way to ping the other end of the tunnel.

Use DVMRP when a router connects to a mrouted router to run DVMRP over a tunnel. It is required to configure Protocol-Independent Multicast (PIM) and an IP address on a DVMRP tunnel.

Generic route encapsulation (GRE) tunneling can be done between our routers only. When using GRE tunneling for AppleTalk, you configure the tunnel with an AppleTalk network address. This means that you can ping the other end of the tunnel.

For multipoint GRE tunnels, a tunnel key must be configured. Unlike other tunnels, the tunnel destination is optional. However, if the tunnel destination is supplied, it must map to an IP multicast address.

Examples

The following example enables Cayman tunneling:

interface tunnel 0 tunnel source ethernet 0 tunnel destination 131.108.164.19 tunnel mode cayman

The following example enables GRE tunneling:

interface tunnel 0 appletalk cable-range 4160-4160 4160.19 appletalk zone Engineering tunnel source ethernet0 tunnel destination 131.108.164.19 tunnel mode gre ip
Related Commands

A dagger (†) indicates that the command is documented in another chapter.

appletalk cable-range
appletalk zone
tunnel destination
tunnel source


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Posted: Mon Oct 21 11:19:49 PDT 2002
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