IP Routing Protocols Commands

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

You can implement aggregate routing in BGP either by redistributing an aggregate route into BGP or by using this conditional aggregate routing feature.

Using the aggregate-address command with no arguments will create an aggregate entry in the BGP routing table if there are any more-specific routes available that fall in the specified range. The aggregate route will be advertised as coming from your autonomous system and has the atomic aggregate attribute set to show that information might be missing. (By default, the atomic aggregate attribute is set unless you specify the as-set keyword in the aggregate-address command.)

Using the as-set keyword creates an aggregate entry using the same rules that the command follows without this keyword, but the path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized. Do not use this form of aggregate-address when aggregating many paths, because this route must be continually withdrawn and re-updated as autonomous system path reachability information for the summarized routes changes.

Using the summary-only keyword not only creates the aggregate route (for example, 193.*.*.*) but will also suppress advertisements of more specific routes to all neighbors. If you only want to suppress advertisements to certain neighbors, you may use the neighbor distribute-list command, with caution. If a more-specific route leaks out, all BGP speakers will prefer that route over the less- specific aggregate you are generating (using longest-match routing).

Using the suppress-map keyword creates the aggregate route but suppresses advertisement of specified route maps. You can use the match clauses of route maps to selectively suppress some more specific routes of the aggregate and leave others unsuppressed. IP access lists and autonomous system path access lists match clauses are supported.

Example

In the following example, an aggregate address is created. The path advertised for this route will be an AS_SET consisting of all elements contained in all paths that are being summarized.

Related Commands

match as-path
match ip address
route-map

Syntax Description

Default

Type 0 authentication (no authentication)

Command Mode

Router configuration

Usage Guidelines

Specifying authentication for an area sets the authentication to Type 1 (simple password) as specified in RFC 1247. If this command is not included in the configuration file, authentication of Type 0 (no authentication) is assumed.

The authentication type must be the same for all communication servers in an area. The authentication password for all OSPF communication servers on a network must be the same if they are to communicate with each other via OSPF. Use the ip ospf authentication-key interface configuration command to specify this password.

Example

The following example mandates authentication for areas 0 and 36.0.0.0 of OSPF routing process 201. Authentication keys are also provided.

Related Commands

area default-cost
area stub
ip ospf authentication-key

Syntax Description

Default

Cost of 1

Command Mode

Router configuration

Usage Guidelines

This command is used only on an Area Border Router (ABR) attached to a stub area.

There are two stub area router configuration commands: the stub and default-cost options of the area command. In all communication servers attached to the stub area, the area should be configured as a stub area using the stub option of the area command. Use the default-cost option only on an ABR attached to the stub area. The default-cost option provides the metric for the summary default route generated by the ABR into the stub area.

Example

The following example assigns a default-cost of 20 to stub network 36.0.0.0:

Related Commands

area authentication
area stub

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

Multiple area router configuration commands specifying the range option can be configured. Thus, OSPF can summarize addresses for many different sets of address ranges.

Example

The following example specifies one summary route to be advertised by the communication server acting as an ABR to other areas for all subnets on network 36.0.0.0 and for all hosts on network 192.42.110.0:

Syntax Description

Default

No stub area is defined.

Command Mode

Router configuration

Usage Guidelines

This command must be configured on all communication servers in the stub area. Use the area router configuration command with the default-cost option to specify the cost of a default internal communication server sent into a stub area by a communication server acting as an Area Border Router (ABR).

There are two stub area router configuration commands: the stub and default-cost options of the area router configuration command. In all communication servers attached to the stub area, the area should be configured as a stub area using the stub option of the area command. Use the default-cost option only on an ABR attached to the stub area. The default-cost option provides the metric for the summary default route generated by the ABR into the stub area.

Example

The following example assigns a default cost of 20 to stub network 36.0.0.0:

Related Commands

area authentication
area default-cost

Syntax Description

Default

area-id: No area ID is predefined.
router-id: No router ID is predefined.
hello-interval seconds: 10 seconds
retransmit-interval seconds: 10 seconds
transmit-delay seconds: 1 second
dead-interval seconds: 40 seconds
authentication-key password: No password is predefined.

Command Mode

Router configuration

Usage Guidelines

In OSPF, all areas must be connected to a backbone area. If the connection to the backbone is lost, it can be repaired by establishing a virtual link.

The smaller the Hello interval, the faster topological changes will be detected, but more routing traffic will ensue.

The setting of the retransmit interval should be conservative, or needless retransmissions will result. The value should be larger for serial lines and virtual links.

The transmit delay value should take into account the transmission and propagation delays for the interface.

A communication server will use the specified authentication key only when authentication is enabled for the backbone with the area area-id authentication router configuration command.

Any keywords and arguments you specify after the authentication-key password keyword-argument pair are ignored. Therefore, specify any optional arguments before this keyword-argument pair.

Example

The following example establishes a virtual link with default values for all optional parameters:

Related Command

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

area authentication
service password-encryption ^†
show ip ospf

Syntax Description

Default

No local autonomous system is specified.

Command Mode

Global configuration

Usage Guidelines

Before you can set up EGP routing, you must specify an autonomous system number. The local autonomous system number will be included in EGP messages sent by the communication server.

Example

The following sample configuration specifies an autonomous system number of 110:

Related Command

router egp

Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Router configuration

Usage Guidelines

By default, BGP does not accept subnets redistributed from IGP. To advertise and carry subnet routes in BGP, use an explicit network command or the no auto-summary command. If you disable auto-summarization and have not entered a network command, you will not advertise network routes for networks with subnet routes unless they contain a summary route.

IP Enhanced IGRP summary routes are given an administrative distance value of 5. You cannot configure this value.

Example

In the following example, network numbers are not summarized automatically:

The following example disables automatic summarization for router process eigrp 109:

Related Command

ip summary-address eigrp

Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Router configuration

Example

In the following example, the automatic resetting of BGP sessions is disabled:

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:

Syntax Description

Command Mode

EXEC

Usage Guidelines

Use this command whenever any of the following changes occur:

• Additions or changes to the BGP-related access lists
  
  
• Changes to BGP-related weights
  
  
• Changes to BGP-related distribution lists
  
  
• Changes in the BGP timer's specifications
  
  
• Changes to the BGP administrative distance
  
  

Example

The following example resets all current BGP sessions:

Related Commands

show ip bgp
timers bgp

Syntax Description

Command Mode

EXEC

Example

The following example removes the neighbor whose address is 160.20.8.3:

Related Command

show ip eigrp neighbors

Syntax Description

Command Mode

EXEC

Usage Guidelines

The IGMP cache contains a list of the multicast groups of which hosts on the directly connected LAN are members. If the communication server has joined a group, it is also listed in the cache.

To delete all entries from the IGMP cache, specify the clear ip igmp group command with no arguments.

Example

The following example clears entries for the multicast group 224.0.255.1 from the IGMP cache:

Related Commands

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

ip host ^†
show ip igmp groups
show ip igmp interface

Syntax Description

Command Mode

EXEC

Examples

The following example deletes all entries from the IP multicast routing table:

The following example deletes from the IP multicast routing table all sources on the 10.3.0.0 subnet that are transmitting to the multicast group 224.2.205.42. Note that this example deletes all sources on network 10.3, not individual sources.

Related Commands

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

ip host ^†
show ip mroute

Syntax Description

Command Mode

EXEC

Example

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

Related Command

show ip route

Syntax Description

Default

Normally, exterior routes are always accepted and default information is passed between IGRP processes when doing redistribution.

Command Mode

Router configuration

Usage Guidelines

The default network of 0.0.0.0 used by RIP cannot be redistributed by IGRP or IP Enhanced IGRP.

Example

The following example allows IGRP exterior or default routes to be received by the IGRP process in autonomous system 23:

The following example allows IP Enhanced IGRP exterior or default routes to be received by the IP Enhanced IGRP process in autonomous system 23:

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

The same functionality will result from the network 0.0.0.0 command, using the network router configuration command.

Example

The following example configures BGP to redistribute network 0.0.0.0 into BGP:

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

Because EGP can use network 0.0.0.0 as a default route, EGP must be explicitly configured to generate a default route. If the next hop for the default route can be advertised as a third party, it will be included as a third party.

Example

The following example configures EGP to generate a default route:

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

When you use this command for the OSPF process, the default network must reside in the routing table and you must satisfy the route-map map-name keyword. Use the default-information originate always route-map map-name form of the command when you do not want the dependency on the default network in the routing table.

Examples

The following example specifies a metric of 100 for the default route redistributed into the OSPF routing domain and an external metric type of Type 1:

Related Command

redistribute

Syntax Description

Default

Built-in, automatic metric translations, as appropriate for each routing protocol

Command Mode

Router configuration

Usage Guidelines

This command is used in conjunction with the redistribute router configuration command to cause the current routing protocol to use the same metric value for all redistributed routes. A default metric helps solve the problem of redistributing routes with incompatible metrics. Whenever metrics do not convert, using a default metric provides a reasonable substitute and enables the redistribution to proceed.

In BGP, this sets the MULTI_EXIT_DISC metric. (The name of this metric for BGP Versions 2 and 3 is INTER_AS.)

Example

The following example shows a communication server in autonomous system 109 using both the RIP and the IGRP routing protocols. The example advertises IGRP-derived routes using the RIP protocol and assigns the IGRP-derived routes a RIP metric of 10.

Related Command

redistribute

Syntax Description

Default

Built-in, automatic metric translations

Command Mode

Router configuration

Usage Guidelines

IGRP metric defaults have been carefully set to work for a wide variety of networks. Take great care in changing these values.

Automatic metric translations for IGRP are only supported when redistributing from IGRP or static.

Example

The following example takes redistributed RIP metrics and translates them into IGRP metrics with values as follows: bandwidth = 1000, delay = 100, reliability = 250, loading = 100, and mtu =1500.

Related Command

redistribute

Syntax Description

Default

Command Mode

Router configuration

Usage Guidelines

Numerically, an administrative distance is an integer between 0 and 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.

When the optional access list number is used with this command, it is applied when a network is being inserted into the routing table. This behavior allows filtering of networks according to the IP address of the communication server supplying the routing information. This could be used, as an example, to filter out possibly incorrect routing information from communication servers not under your administrative control.

The order in which you enter distance commands can affect the assigned administrative distances in unexpected ways (see "Example" for further clarification).

Weight values are also subjective; there is no quantitative method for choosing weight values.

For BGP, the distance command sets the administrative distance of the External BGP route.

The show ip protocols EXEC command displays the default administrative distance for a specified routing process.

Example

In the following example, the router igrp global configuration command sets up IGRP routing in autonomous system number 109. The network router configuration commands specify IGRP routing on networks 192.31.7.0 and 128.88.0.0. The first distance router configuration command sets the default administrative distance to 255, which instructs the communication server to ignore all routing updates from communication servers for which an explicit distance has not been set. The second distance command sets the administrative distance for all communication servers on the Class C network 192.31.7.0 to 90. The third distance command sets the administrative distance for the communication server with the address 128.88.1.3 to 120.

Related Command

distance bgp

Syntax Description

Default

external-distance: 20
internal-distance: 200
local-distance: 200

Command Mode

Router configuration

Usage Guidelines

An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual communication server or a group of communication servers. Numerically, an administrative distance is an integer between 0 and 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.

Use this command if another protocol is known to be able to provide a better route to a node than was actually learned via external BGP, or if some internal routes should really be preferred by BGP.

Example

In the following example, internal routes are known to be preferable to those learned through the IGP, so the administrative distance values are set accordingly:

Related Command

distance

Syntax Description

Default

internal-distance: 90
external-distance: 170

Command Mode

Router configuration

Usage Guidelines

An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual communication server or a group of communication servers. Numerically, an administrative distance is an integer between 0 and 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.

Use the distance eigrp command if another protocol is known to be able to provide a better route to a node than was actually learned via external IP Enhanced IGRP or if some internal routes should really be preferred by IP Enhanced IGRP.

To display the default administrative distance for a specified routing process, use the show ip protocols EXEC command.

Example

In the following example, the router eigrp global configuration command sets up IP Enhanced IGRP routing in autonomous system number 109. The network router configuration commands specify IP Enhanced IGRP routing on networks 192.31.7.0 and 128.88.0.0. The first distance router configuration command sets the default administrative distance to 255, which instructs the communication server to ignore all routing updates from communication servers for which an explicit distance has not been set. The second distance router configuration command sets the administrative distance for all communication servers on the Class C network 192.31.7.0 to 90. The third distance router configuration command sets the administrative distance for the communication server with the address 128.88.1.3 to 120.

Related Command

show ip protocols

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

If no interface is specified, the access list will be applied to all incoming updates.

Example

The following example causes only two networks to be accepted by a RIP routing process: network 0.0.0.0 (the RIP default) and network 131.108.0.0.

Related Commands

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

access-list †
distribute-list out
redistribute

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

When redistributing networks, a routing process name can be specified as an optional trailing argument to the distribute-list command. This causes the access list to be applied to only those routes derived from the specified routing process. After the process-specific access list is applied, any access list specified by a distribute-list command without a process name argument will be applied. Addresses not specified in the distribute-list command will not be advertised in outgoing routing updates.

Examples

The following example would cause only one network to be advertised by a RIP routing process: network 131.108.0.0.

Related Commands

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

access-list †
distribute-list in
redistribute

Syntax Description

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

The optional keyword secondary allows an unlimited number of secondary addresses to be specified. Secondary addresses are treated like primary addresses, except that the system never generates datagrams other than routing updates with secondary source addresses. IP broadcasts and ARP requests are handled properly, as are interface routes in the IP routing table.

Example

The following example specifies 131.108.1.27 as the primary address and 192.31.7.17 as a secondary address for Ethernet interface 0:

Syntax Description

Default

No access lists are defined.

Command Mode

Global configuration

Usage Guidelines

You can specify an access list filter on both inbound and outbound BGP routes. In addition, you can assign weights based on a set of filters. Each filter is an access list based on regular expressions. If the regular expression matches the representation of the autonomous system path of the route as an ASCII string, then the permit or deny condition applies. The autonomous system path does not contain the local autonomous system number. Use the ip as-path access-list global configuration command to define an BGP access list, and the neighbor router configuration command to apply a specific access list.

See the "Regular Expressions" appendix for information on forming regular expressions.

Example

The following example specifies that the BGP neighbor with IP address 128.125.1.1 is not sent advertisements about any path through or from the adjacent autonomous system 123:

Related Commands

neighbor distribute-list
neighbor filter-list

Syntax Description

Default

Once you permit a value for the community number, the community list defaults to an implicit deny for everything else that has not been permitted.

Command Mode

Global configuration

Example

In the following example, the communication server permits all routes except the routes with the communities 5 and 10 or 10 and 15:

Related Command

set community

Syntax Description

Default

If the communication server has a directly connected interface onto the specified network, the dynamic routing protocols running on that communication server will generate (or source) a default route. For RIP, this is flagged as the pseudonetwork 0.0.0.0; for IGRP, it is the network itself, flagged as an exterior route.

Command Mode

Global configuration

Usage Guidelines

The communication server uses both administrative distance and metric information to determine the default route. Multiple ip default-network commands can be given. All candidate default routes, both static (that is, flagged by ip default-network) and dynamic, appear in the routing table preceded by an asterisk.

If the IP routing table indicates that the specified network number is subnetted and a non-zero subnet number is specified, then the system will automatically configure a static summary route. This static summary route is configured instead of a default network. The effect of the static summary route is to cause traffic destined for subnets that are not explicitly listed in the IP routing table to be routed using the specified subnet.

Examples

The following example defines a static route to network 10.0.0.0 as the static default route:

If the following command was issued on a communication server not connected to network 129.140.0.0, the communication server might choose the path to that network as a default route when the network appeared in the routing table:

Related Command

show ip route

Syntax Description

Default

All destinations are accepted with a distance of 0.

Command Mode

Interface configuration

Usage Guidelines

Any sources that match the access list are stored in the DVMRP routing table.

The route with the lower distance (either the route in the unicast routing table or that in the DVMRP routing table) takes precedence when computing the Reverse Path Forwarding (RPF) interface for a source of a multicast packet.

By default, the administrative distance for DVMRP routes is 0. This means that they always take precedence over unicast routing table routes. If you have two paths to a source, one through unicast routing (using PIM as the multicast routing protocol) and another path using DVMRP (unicast and multicast routing), and if you want to use the PIM path, use the ip dvmrp accept-filter command to increase the administrative distance for DVMRP routes. For example, if the unicast routing protocol is Enhanced IGRP, which has a default administrative distance of 90, you could define and apply the following access list so the RPF interface used to accept multicast packets will be through the Enhanced IGRP/PIM path:

Example

The following example applies access list 57 to the interface and sets a distance of 4:

Related Commands

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

distance
ip dvmrp metric
show ip dvmrp route
tunnel mode ^†

Syntax Description

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

You can use the ip dvmrp metric command with the ip dvmrp default-information command to tailor the metric used when advertising the default route 0.0.0.0. By default, metric 1 is used.

Example

The following example configures the communication server to advertise network 0.0.0.0, in addition to other networks, to DVMRP neighbors:

Related Command

ip dvmrp metric

Syntax Description

Default

No metric is preconfigured. Only directly connected subnets and networks are advertised to neighboring DVMRP communication servers.

Command Mode

Interface configuration

Usage Guidelines

When PIM is configured on an interface and DVMRP neighbors are discovered, the communication server sends DVMRP report messages for directly connected networks. The ip dvmrp metric command enables DVMRP report messages for multicast destinations that match the access list. Usually, the metric for these routes is 1. Under certain circumstances, it may be desirable to tailor the metric used for various unicast routes.

Use the access-list-number argument in conjunction with the protocol process-id arguments to selectively list the destinations learned from a given routing protocol.

If you do not specify this command, only directly connected subnets are advertised via DVMRP.

To display DVMRP activity, use the debug ip dvmrp command.

Example

The following example connects a PIM cloud to a DVMRP cloud. Access list 1 permits the sending of DVMRP reports to the DVMRP communication servers advertising all sources in the 198.92.35.0 network with a metric of 1. Access list 2 permits all other destinations, but the metric of 0 means that no DVMRP reports are sent for these destinations.

Related Commands

A dagger (†) indicates that the command is documented in the Debug Command Reference publication.

debug ip dvmrp ^†
ip dvmrp accept-filter

Syntax Description

Default

priority = 100
reporttime = 5 seconds for broadcast media; 0 for nonbroadcast media
holdtime = 15 seconds

Command Mode

Interface configuration

Usage Guidelines

When enabled on an interface, GDP updates report the primary and secondary IP addresses of that interface.

Example

In the following example, GDP is enabled on Ethernet interface 1 with a report time of 10 seconds, and priority and hold time set to their defaults (because none are specified):

Syntax Description

Default

5 seconds

Command Mode

Interface configuration

Example

The following example sets the hello interval for Ethernet interface 0 to 10 seconds:

Related Command

ip hold-time eigrp

Syntax Description

Default

15 seconds

Command Mode

Interface configuration

Usage Guidelines

The hold time is three times the hello interval. If the current value for the hold time is less than two times the hello interval, the hold time is reset.

If a communication server does not receive a hello packet within the specified hold time, routes through the communication server are considered available.

Increasing the hold time delays route convergence across the network.

Example

The following example sets the hold time for Ethernet interface 0 to 40 seconds:

Related Command

ip hello-interval eigrp

Syntax Description

Default

All groups are allowed on an interface.

Command Mode

Interface configuration

Example

In the following example, host services by Ethernet interface 0 can join the group 225.2.2.2 only:

Related Command

ip igmp join-group

Syntax Description

Default

No multicast group memberships are predefined.

Command Mode

Interface configuration

Usage Guidelines

IP packets that are addressed to the group address are passed to the IP client process in the communication server.

If all the multicast-capable communication servers that you administer are members of a multicast group, pinging that group causes all communication servers to respond. This can be a useful administrative and debugging tool.

Another reason to have a communication server join a multicast group is when other hosts on the network have a bug in IGRP that prevents them from correctly answering IGMP queries. Having the communication server join the multicast group causes upstream communication servers to maintain multicast routing table information for that group and keeps the paths for that group active.

Example

In the following example, the communication server joins multicast group 225.2.2.2:

Related Commands

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

ip igmp access-group
ping ^†

Syntax Description

Default

60 seconds

Command Mode

Interface configuration

Usage Guidelines

Multicast communication servers send host membership query messages (referred to as host-query messages) to discover which multicast groups have members on the communication server's attached networks. Hosts respond with IGMP report messages indicating that they wish to receive multicast packets for specific groups (that is, indicating that the host wants to become a member of the group). Host-query messages are addresses to the all-hosts multicast group, which has the address 224.0.0.1, and have an IP TTL value of 1.

The designated router for a LAN is the only communication server that sends IGMP host-query messages. The designated router is elected according to the multicast routing protocol that runs on the LAN.

Example

The following example changes the frequency at which the designated router sends IGMP host-query messages to 2 minutes:

Related Commands

ip pim query-interval
show ip igmp groups

Syntax Description

Default

Disabled

When enabled, IRDP uses these defaults:

• Broadcast IRDP advertisements
  
  
• Maximum interval between advertisements: 600 seconds
  
  
• Minimum interval between advertisements: 0.75 times maxadvertinterval
  
  
• Preference: 0
  
  

Command Mode

Interface configuration

Usage Guidelines

If you change maxadvertinterval, the other two values also change, so it is important to change maxadvertinterval first before changing either holdtime or minadvertinterval.

Example

The following example illustrates how to set the various IRDP processes:

Syntax Description

This command has no keywords or arguments.

Default

IP multicast routing is disabled.

Command Mode

Global configuration

Usage Guidelines

When IP multicast routing is disabled, the communication server does not forward any multicast packets.

Example

The following example enables IP multicast routing on the communication server:

Related Command

ip pim

Syntax Description

Default

0, which means that all multicast packets are forwarded on the interface.

Command Mode

Interface configuration

Usage Guidelines

Any multicast packets with a TTL value less than the threshold are not forwarded out the interface.

You should configure the TTL threshold only on border routers. Conversely, communication servers on which you configure a TTL threshold value automatically become border routers.

Example

In the following example, you set the TTL threshold on a border router to 200, which is a very high value. This means that multicast packets must have a TTL greater than 200 in order to be forwarded out this interface. Multicast applications generally set this value well below 200. Therefore, setting a value of 200 means that no packets will be forwarded out the interface.

Syntax Description

Default

No password is specified.

Command Mode

Interface configuration

Usage Guidelines

The password created by this command is used as a "key" that is inserted directly into the OSPF header when the communication server originates routing protocol packets. A separate password can be assigned to each network on a per-interface basis. All neighboring communication servers on the same network must have the same password to be able to exchange OSPF information.

Example

In the following example, the authentication key is enabled with the string yourpass:

Related Command

area authentication

Syntax Description

Default

No default cost is predefined.

Command Mode

Interface configuration

Usage Guidelines

Unlike IGRP, you must set this metric manually using this command, if you need to change the default. Changing the bandwidth does not change the link cost.

The link state metric is advertised as the link cost in the communication server's router link advertisement. We do not support Type of Service (TOS), so you can assign only one cost per interface.

In general, the path cost is calculated as follows:

     10⁸ ÷ Bandwidth

Using the above formula, the default path costs were calculated as noted in the following list. If these values do not suit your network, you can use your own method of calculating path costs.

• 56-kbps Serial Link—Default cost is 1785
  
  
• 64-kbps Serial Link—Default cost is 1562
  
  
• T1 (1.544-Mbps Serial Link)—Default cost is 65
  
  
• E1 (2.048-Mbps Serial Link)—Default cost is 48
  
  
• 4-Mbps Token Ring—Default cost is 25
  
  
• Ethernet—Default cost is 10
  
  
• 16-Mbps Token Ring—Default cost is 6
  
  
• FDDI—Default cost is 1
  
  

Example

The following example sets the interface cost value to 65:

Syntax Description

Default

Four times the interval set for the ip ospf hello-interval command

Command Mode

Interface configuration

Usage Guidelines

The interval is advertised in the communication server's Hello packets. This value must be the same for all communication servers on a specific network.

Example

The following example sets the OSPF dead interval to 60 seconds:

Related Command

ip ospf hello-interval

Syntax Description

Default

10 seconds

Command Mode

Interface configuration

Usage Guidelines

This value is advertised in the communication server's Hello packets. The smaller the Hello interval, the faster topological changes will be detected, but more routing traffic will ensue. This value must be the same for all communication servers on a specific network.

Example

The following example sets the interval between Hello packets to 15 seconds:

Related Command

ip ospf dead-interval

Syntax Description

Default

Depends on the network type

Command Mode

Interface configuration

Usage Guidelines

Using this feature, you can configure broadcast networks as nonbroadcast multiaccess networks when, for example, you have communication servers in your network that do not support multicast addressing. You can also configure nonbroadcast multiaccess networks, such as X.25, Frame Relay, and SMDS, as broadcast networks. This feature saves you from having to configure neighbors.

If this command is issued on an interface that does not allow it, it will be ignored.

Example

The following example sets your OSPF network as a broadcast network:

Related Commands

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

frame-relay map ^†
neighbor (OSPF)
x25-map ^†

Syntax Description

Default

Priority of 1

Command Mode

Interface configuration

Usage Guidelines

When two communication servers attached to a network both attempt to become the designated communication server; the one with the higher priority takes precedence. If there is a tie, the communication server with the higher ID takes precedence. A communication server with a priority set to zero is ineligible to become the designated communication server or backup designated communication server. Communication server priority is only configured for interfaces to multiaccess networks (in other words, not point-to-point networks).

This priority value is used when you configure OSPF for nonbroadcast networks using the neighbor router configuration command for OSPF.

Example

The following example sets the communication server priority value to 4:

Related Commands

ip ospf network
neighbor (OSPF)

Syntax Description

Default

5 seconds

Command Mode

Interface configuration

Usage Guidelines

When a communication server sends a link state advertisement (LSA) to its neighbor, it keeps the LSA until it receives back the acknowledgment. If it receives no acknowledgment in seconds, it will retransmit the LSA.

The setting of this parameter should be conservative, or needless retransmission will result. The value should be larger for serial lines and virtual links.

Example

The following example sets the retransmit-interval value to 8 seconds:

Syntax Description

Default

1 second

Command Mode

Interface configuration

Usage Guidelines

Link state advertisements in the update packet must have their age incremented by the amount specified in the seconds argument before transmission. The value assigned should take into account the transmission and propagation delays for the interface.

If the delay is not added before transmission over a link, the time in which the LSA propagates over the link is not considered. This setting has more significance on very low speed links.

Example

The following example sets the retransmit-delay value to 3 seconds:

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

This feature makes it easier to identify a communication server because it is displayed by name rather than by its communication server ID or neighbor ID.

Example

The following example configures OSPF to look up DNS names for use in all OSPF show EXEC command displays:

Sample Display

The following is sample output of the show ip ospf database EXEC command, for example, once you have enabled the DNS name lookup feature.

Syntax Description

Default

IP multicast routing is disabled on all interfaces.

There is no default mode setting.

Command Mode

Interface configuration

Usage Guidelines

Enabling PIM on an interface also enables IGMP operation on that interface. An interface can be configured to be in dense mode or sparse mode. The mode describes how the communication server populates its multicast routing table and how the communication server forwards multicast packets it receives from its directly connected LANs. In populating the multicast routing table, dense-mode interfaces are always added to the table. Sparse-mode interfaces are added to the table only when periodic join messages are received from downstream communication servers or there is a directly connected member on the interface.

Initially, a dense-mode interface forwards multicast packets until the communication server determines that there are group members or downstream communication servers, or until a prune message is received from a downstream communication server. Then, the dense-mode interface will periodically forward multicast packets out the interface until the same conditions occur. Dense mode assumes that there are multicast group members present. Dense-mode communication servers never send a join message. They do send prune messages as soon as they determine they have no members or downstream PIM communication servers.

A sparse-mode interface is used only for multicast forwarding if a join message is received from a downstream communication server or if there are group members directly connected to the interface. Sparse mode assumes that there are no other multicast group members present. When sparse-mode communication servers want to join the shared path, they periodically send join messages toward the RP. When sparse-mode communication servers want to join the source path, they periodically send join messages toward the source; they also send periodic prune messages toward to RP to prune the shared path.

Examples

The following command enables sparse-mode PIM on tunnel interface 0 and sets the address of the RP communication server to 226.0.0.8:

The following commands enable dense-mode PIM multicast routing on Ethernet interface 1:

Related Commands

ip multicast-routing
ip pim rp-address
show ip igmp interface

Syntax Description

Default

60 seconds

Command Mode

Global configuration

Usage Guidelines

The join-and-prune message interval should be the same for all communication servers in the internetwork.

A communication server is pruned from a group if a join message is not heard from it in three times the message interval specified by the seconds argument. By default, this is 3 minutes.

Example

The following example changes the PIM message interval to 90 seconds:

Related Commands

ip igmp query-interval
ip pim query-interval

Syntax Description

Default

30 seconds

Command Mode

Interface configuration

Usage Guidelines

Routers that are configured for IP multicast send PIM router-query messages to determine which communication server will be the designated router for each LAN segment (subnet). The designated router is responsible for sending IGMP host-query messages to all hosts on the directly connected LAN. When operating in sparse mode, the designated router is responsible for sending source registration messages to the RP. The designated router is the communication server with the largest IP address.

Example

The following example changes the PIM router-query message interval to 45 seconds:

Related Command

ip igmp query-interval
ip pim message-interval

Syntax Description

Default

No PIM RPs are preconfigured.

Command Mode

Global configuration

Usage Guidelines

You must configure the IP address of RPs in leaf routers only. Leaf routers are those communication servers that are directly connected either to a multicast group member or to a sender of multicast messages.

The RP address is used by first-hop communication servers to send register packets on behalf of source multicast hosts to the RP. This address is also used by communication servers on behalf of multicast hosts that want to become members of a group to send join messages towards the RP. The RP must be a PIM communication server; however, it does not require any special configuration to recognize that it is the RP. Also, RPs are not members of the multicast group; rather, they serve as a "meeting place" for multicast sources and group members.

Choosing the communication server that will be an RP requires prior coordination between the people who want to be members of the multicast group. You should examine the length of the paths between members and sources. Remember that most multicast members will eventually want to join to the source tree that is the shortest route between the source and the group member.

You can configure a communication server to use a single RP for more than one group. The conditions specified by the access list determine which groups the RP can be used for. If no access list is configured, the RP is used for all groups.

A PIM communication server can use multiple RPs.

First-hop communication servers for multicast sources send register packets to all configured RPs. First-hop communication servers for multicast group members send join packets to one RP at a time. Once this communication server begins receiving multicast packets for the group, it will have joined one RP tree. Because the communication server does not want to receive multiple copies of the same packet, it joins only one RP tree.

Examples

The following example sets the PIM RP address to 198.92.37.33 for all multicast groups:

The following example sets the PIM RP address to 147.106.6.22 for the multicast group 225.2.2.2 only:

Related Command

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

access-list ^†

Syntax Description

Default

No static routes are established.

Command Mode

Global configuration

Usage Guidelines

A static route is appropriate when the communication server cannot dynamically build a route to the destination.

If you specify an administrative distance, you are flagging a static route that can be overridden by dynamic information. For example, IGRP-derived routes have a default administrative distance of 100. To have a static route that would be overridden by an IGRP dynamic route, specify an administrative distance greater than 100. Static routes have a default administrative distance of 1.

Static routes that point to an interface will be advertised via RIP, IGRP, and other dynamic routing protocols, regardless of whether redistribute static commands were specified for those routing protocols. This is because static routes that point to an interface are considered in the routing table to be connected and hence lose their static nature. However, if you define a static route to an interface that is not one of the networks defined in a network command, no dynamic routing protocols will advertise the route unless a redistribute static command is specified for these protocols.

Examples

In the following example, an administrative distance of 110 was chosen. In this case, packets for network 10.0.0.0 will be routed through to the communication server at 131.108.3.4 if dynamic information with administrative distance less than 110 is not available.

In the following example, packets for network 131.108.0.0 will be routed to the communication server at 131.108.6.6:

Syntax Description

This command has no arguments or keywords.

Default

Varies with media

Command Mode

Interface configuration

Usage Guidelines

If split horizon has been disabled on an interface and you wish to enable it, use the ip split-horizon command to restore the split horizon mechanism.

Example

The following example illustrates a simple example of disabling split horizon on a serial link. In this example, the serial link is connected to an X.25 network:

Syntax Description

Default

Enabled

Command Mode

Interface configuration

Usage Guidelines

For networks that include links over X.25 PSNs, you can use the neighbor router configuration command to defeat the split horizon feature. As an alternative, you can explicitly specify the no ip split-horizon eigrp command in your configuration. However, if you do so, you must similarly disable split horizon for all communication servers in any relevant multicast groups on that network.

In general, it is recommended that you not change the default state of split horizon unless you are certain that your application requires the change in order to properly advertise routes. Remember that if split horizon is disabled on a serial interface and that interface is attached to a packet-switched network, you must disable split horizon for all communication servers in any relevant multicast groups on that network.

Example

The following example disables split horizon on a serial link connected to an X.25 network:

Related Commands

ip split-horizon
neighbor

Syntax Description

Default

No summary aggregate addresses are predefined.

Command Mode

Interface configuration

Usage Guidelines

IP Enhanced IGRP summary routes are given an administrative distance value of 5. You cannot configure this value.

Example

The following example sets the IP summary aggregate address for Ethernet interface 0:

Related Command

auto-summary

Syntax Description

Default

No community list is defined.

Command Mode

Route-map configuration

Usage Guidelines

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want to modify only some data, you must configure a second route-map section with an explicit match specified.

Matching based on community list is one of the types of match clauses applicable to BGP.

Examples

In the following example, the routes that match community list 1 will have the weight set to 100. Any route that has community 109 will have the weight set to 100.

In the following example, the routes that match community list 1 will have the weight set to 200. Any route that has community 109 alone will have the weight set to 200.

Related Commands

ip community-list
route-map
set weight

Syntax Description

Default

No match interfaces are defined.

Command Mode

Route-map configuration

Usage Guidelines

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want o modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, routes that have their next hop out Ethernet interface 0 will be distributed:

Related Commands

route-map
set

Syntax Description

Default

No access list numbers are specified.

Command Mode

Route-map configuration

Usage Guidelines

Use the route-map global configuration command, and the route-map configuration commands match and set, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want o modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, routes that have addresses specified by access list numbers 5 and 80 will be distributed:

Related Commands

route-map
set

Syntax Description

Default

Routes are distributed freely, without being required to match a next-hop address.

Command Mode

Route-map configuration

Usage Guidelines

Use the route-map global configuration command, and the route-map configuration commands match and set, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want o modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, routes that have a next-hop communication server address passed by access list 5 or 80 will be distributed:

Related Commands

route-map
set

Syntax Description

Default

No filtering on route source.

Command Mode

Route-map configuration

Usage Guidelines

Use the route-map global configuration command, and the route-map configuration commands match and set, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria— the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want o modify only some data, you must configure second route-map section with an explicit match specified.

There are situations in which a route's next hop and source communication server address are not the same.

Example

In the following example, routes that have been advertised by communication servers at the addresses specified by access lists 5 and 80 will be distributed:

Related Commands

route-map
set

Syntax Description

Default

No filtering on a metric value.

Command Mode

Route-map configuration

Usage Guidelines

Use the route-map global configuration command, and the route-map configuration commands match and set, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want o modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, routes with the metric 5 will be redistributed.

Related Commands

route-map
set

Syntax Description

Default

Disabled

Command Mode

Route-map configuration

Usage Guidelines

Use the route-map global configuration command, and the route-map configuration commands match and set, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions that you should perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want to modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, internal routes will be redistributed:

Related Commands

route-map
set

Syntax Description

Default

Disabled

Command Mode

Route-map configuration

Usage Guidelines

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" before the route is redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route- map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want to modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, internal routes will be redistributed:

Related Commands

route-map
set

Syntax Description

Default

No match tag values are defined.

Command Mode

Route-map configuration

Usage Guidelines

Use the route-map global configuration command, and the route-map configuration commands match and set, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

The match route-map configuration command has multiple formats. The match commands may be given in any order, and all match commands must "pass" to cause the route to be redistributed according to the set actions given with the set commands. The no forms of the match commands remove the specified match criteria.

A route map can have several parts. Any route that does not match at least one match clause relating to a route-map command will be ignored; that is, the route will not be advertised for outbound route maps and will not be accepted for inbound route maps. If you want o modify only some data, you must configure second route-map section with an explicit match specified.

Example

In the following example, routes stored in the routing table with tag 5 will be redistributed:

Related Commands

route-map
set

Syntax Description

Command Mode

EXEC

Usage Guidelines

The mbranch command sends multicast IGMP trace request packets to the specified branch communication server. It displays information about the branch starting with the local (requesting) communication server and ending with the branch communication server. This is considered to be the forward direction.

The information returned shows how a multicast packet sourced by this communication server will be forwarded by each communication server on the path to the communication server with the branch address.

The communication server with the address branch-address is the only communication server that responds to the trace request packets. The response is unicast to the source.

It is important to specify a value for the ttl argument if you are tracing through a communication server on which a multicast threshold has been set with the ip multicast-threshold interface configuration command.

Sample Display

The following is sample output from the mbranch command. This trace is between the same communication servers as shown in the example for the mrbranch command. Note the order of responses. Also note that the outgoing interface list is the same.

Related Commands

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

ip multicast-threshold
mbranch ^†

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

Holddown keeps new routing information from being used for a certain period of time. This can prevent routing loops caused by slow convergence. It is sometimes advantageous to disable holddown to increase the network's ability to quickly respond to topology changes; this command provides this function.

Use the metric holddown command if other communication servers within the IGRP autonomous system are not configured with no metric holddown. If all communication servers are not configured the same way, you increase the possibility of routing loops.

Example

The following example disables metric holddown:

Related Commands

metric maximum-hops
metric weights
timers basic

Syntax Description

Default

100 hops

Command Mode

Router configuration

Usage Guidelines

This command provides a safety mechanism that breaks any potential count-to-infinity problems. It causes the IP routing software to advertise as unreachable routes with a hop count greater than the value assigned to the hops argument.

Example

In the following example, a communication server in autonomous system 71 attached to network 15.0.0.0 wants a maximum hop count of 200, doubling the default. The network administrators decided to do this because they have a complex WAN that can generate a large hop count under normal (nonlooping) operations.

Related Commands

metric holddown
metric weights

Syntax Description

Default

tos=0
k1 = 1
k2 = 0
k3 = 1
k4 = 0
k5 = 0

Command Mode

Router configuration

Usage Guidelines

Use this command to alter the default behavior of IGRP routing and metric computation and allow the tuning of the IGRP metric calculation for a particular type of service (TOS).

If k5 equals 0, the composite IGRP metric is computed according to the following formula:

If k5 does not equal zero, an additional operation is done:

Bandwidth is inverse minimum bandwidth of the path in bits per second scaled by a factor of 10*10¹⁰. The range is from a 1200 bps line to 10 Gbps.

Delay is in units of 10 microseconds. This gives a range of 10 microseconds to 168 seconds. A delay of all ones indicates that the network is unreachable.

The delay parameter is stored in a 24-bit field, in tens of microseconds. Hence, the delay can be from 1 (10 microseconds) to hex FFFFFF (decimal 16777215), which corresponds to 167.77215 seconds. A delay of all ones (that is, a delay of 16777215) indicates that the network is unreachable.

Reliability is given as a fraction of 255. That is, 255 is 100 percent reliability or a perfectly stable link.

Load is given as a fraction of 255. A load of 255 indicates a completely saturated link.

Example

The following example sets the metric weights to slightly different values than the defaults:

Related Commands

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

bandwidth †
delay ^†
metric holddown
metric maximum-hops

Syntax Description

Command Mode

EXEC

Usage Guidelines

The mrbranch command sends trace request packets to the specified branch communication server. Queries are sent recursively to all the communication servers in the branch. This command displays information about the branch starting with the communication server farthest away and working towards the requesting communication server. This is considered to be the reverse direction.

The information returned shows how a multicast packet sourced by this communication server will be forwarded by each communication server along the branch.

The communication server with the address branch-address responds to the trace request packets. The requesting communication server then sends a query to the communication server that is the first communication server's RPF neighbor. Both the request and response packets have unicast addresses.

The number of packets generated by this command is two times the number of communication servers between the source communication server and the specified branch communication server.

Sample Display

The following is sample output from the mrbranch command. This example is between the same communication server as shown in the mbranch command. Note the order of the responses. Also note that the outgoing interface list is the same.

Related Commands

mbranch
show ip mroute

Syntax Description

Command Mode

EXEC

Usage Guidelines

The trace request generated by the mtrace command is multicast to the multicast group. Responses are unicast to the source communication server.

Responses are delayed by the responders.

Sample Display

The following is sample output from the mtrace command:

Related Commands

mbranch
mrbranch

Syntax Description

Default

No neighboring communication servers are defined.

Command Mode

Router configuration

Usage Guidelines

For exterior routing protocol EGP, this command specifies routing peers. For normally broadcast protocols such as IGRP or RIP, this command permits the point-to-point (nonbroadcast) exchange of routing information. When used in combination with the passive-interface router configuration command, routing information can be exchanged between a subset of communication servers on a LAN.

Multiple neighbor commands can be used to specify additional neighbors or peers.

OSPF has its own version of the neighbor command. See the neighbor (OSPF) command page in this chapter.

Examples

The following example establishes an EGP neighbor:

In the following example, IGRP updates are sent to all interfaces on network 131.108.0.0 except Ethernet interface 1. However, in this case a neighbor router configuration command is included. This command permits the sending of routing updates to specific neighbors. One copy of the routing update is generated per neighbor.

Related Command

passive-interface

Syntax Description

Default

No configuration is specified.

Command Mode

Router configuration

Usage Guidelines

X.25 and Frame Relay provide an optional broadcast capability that can be configured in the map to allow OSPF to run as a broadcast network. At the OSPF level you can configure the communication server as a broadcast network. See the x25 map and frame-relay map interface configuration command descriptions in "X.25 Commands" and "Frame Relay Commands" chapters, respectively, of this manual for more detail.

One neighbor entry must be included in the communication server's configuration for each known nonbroadcast network neighbor. The neighbor address has to be on the primary address of the interface.

If a neighboring communication server has become inactive (Hello packets have not been seen for the Router DeadInterval period), it may still be necessary to send Hello packets to the dead neighbor. These Hello packets will be sent at a reduced rate called Poll Interval.

When the communication server first starts up, it sends only Hello packets to those communication servers with non-zero priority, that is, communication servers that are eligible to become designated routers and backup designated routers. After designated routers and backup designated routers are selected, they will then start sending Hello packets to all neighbors in order to form adjacencies.

Example

The following example declares a communication server at address 131.108.3.4 on a nonbroadcast network, with a priority of 1 and a poll-interval of 180:

Related Command

ip ospf priority

Syntax Description

Default

No configuration is specified.

Command Mode

Router configuration

Example

The following example configuration illustrates the use of the neighbor any command in conjunction with the access-list global configuration command:

Related Commands

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

access-list ^†
neighbor any third-party
router egp 0

Syntax Description

Default

No EGP process is configured.

Command Mode

Router configuration

Example

The following example specifies the particular neighbors that an EGP process will view as peers:

Related Commands

neighbor any
router egp 0

Syntax Description

Default

New neighbors are treated as temporary.

Command Mode

Router configuration

Usage Guidelines

Under normal circumstances, neighbors that are allowed to connect to the communication server because you had configured a template are treated as temporary. When a temporary neighbor disconnects, the local communication server will not try to actively reestablish a connection with it. In addition, information about temporary neighbors will not show up in the communication server configuration (write terminal).

When configure-neighbors is enabled on a particular template, any neighbor accepted by that template will be treated as if it had been manually configured. These neighbors will show up in write terminal displays and will be written to the nonvolatile configuration if a write memory command is issued.

Example

In the following example, any BGP speaker matching access-list 7 can connect to the communication server and exchange information. Any neighbor that connects will be treated as if it had been manually configured.

Related Command

neighbor neighbor-list

Syntax Description

Default

No BGP neighbor is specified.

Command Mode

Router configuration

Usage Guidelines

Using distribute lists is one of two ways to filter BGP advertisements. The other way is to use autonomous system-path filters, as with the ip as-path access-list global configuration command and the neighbor
filter-list command.

Example

The following example applies list 39 to incoming advertisements to neighbor 120.23.4.1:

Related Commands

ip as-path access-list
neighbor filter-list

Syntax Description

Default

Only directly connected neighbors are allowed.

Command Mode

Router configuration

Usage Guidelines

This feature should only be used under the guidance of technical support staff.

Example

The following example allows connections to or from neighbor 131.108.1.1, which resides on a network that is not directly connected:

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

This command establishes filters on both inbound and outbound BGP routes. Any number of weight filters are allowed on a per-neighbor basis, but only one in or out filter is allowed. The weight of a route affects BGP's route-selection rules.

The implemented weight is based on the first matched autonomous system path. Weights indicated when an autonomous system path is matched override the weights assigned by global neighbor commands. In other words, the weights assigned with the match as-path and set weight route-map commands override the weights assigned using the neighbor weight and neighbor filter-list commands.

See the "Regular Expressions" appendix for information on forming regular expressions.

Example

In the following example, the BGP neighbor with IP address 128.125.1.1 is not sent advertisements about any path through or from the adjacent autonomous system 123:

Related Commands

ip as-path access-list
neighbor distribute-list
neighbor weight

Syntax Description

Default

No configuration is defined.

Command Mode

Router configuration

Usage Guidelines

To specify a group of anonymous neighbors, configure a neighbor template rather than specifically configure each neighbor. The template allows you to specify an IP access list which defines remote systems that can establish a BGP connection to the communication server. External BGP peers must be on a directly connected Ethernet unless they are overridden by the neighbor ebgp-multihop command.

Once you specify a template, you configure the template as if it were a regular neighbor entry, such as setting the protocol version or filter lists, so that anonymous neighbors accepted by the template will receive the settings of the template.

These neighbors accepted by the template appear in the show ip bgp summary and show ip bgp neighbor displays, although they do not appear in the communication server configuration. When the session is disconnected, all knowledge about the neighbor is discarded and the communication server will not attempt to actively re-establish a connection.

You can use the neighbor configure-neighbors command to request that the communication server treat peers learned through a template as if they were manually configured neighbors. These peers will then show up in write terminal displays and can be stored as part of the nonvolatile configuration.

Examples

In the following example, any BGP speaker from 168.89.3.0 can connect to the communication server and exchange information:

In the following example, any BGP speaker in the connected internet can establish a BGP connection to the local communication server, and the local communication server will send them routing information. However, the distribute-list clause instructs the local communication server to ignore all information these remote BGP speakers send to it.

Related Commands

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

access-list (standard) ^†
neighbor configure-neighbors
neighbor ebgp-multihop

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

This command is useful in nonmeshed networks such as Frame Relay or X.25 where BGP neighbors may not have direct access to all other neighbors on the same IP subnet.

Example

The following example forces all updates destined for 131.108.1.1 to advertise this communication server as the next hop:

Syntax Description

Default

There are no BGP neighbor peers.

Command Mode

Router configuration

Usage Guidelines

Specifying a neighbor with an autonomous system number that matches the autonomous system number specified in the router bgp global configuration command identifies the neighbor as internal to the local autonomous system. Otherwise, the neighbor is considered external.

Examples

The following example specifies that the communication server at the address 131.108.1.2 is a neighbor in autonomous system number 109:

In the following example, a BGP communication server is assigned to autonomous system 109, and two networks are listed as originating in the autonomous system. Then the addresses of three remote communication servers (and their autonomous systems) are listed. The communication server being configured will share information about networks 131.108.0.0 and 192.31.7.0 with the neighbor communication servers. The first communication server listed is in the same Class B network address space, but in a different autonomous system; the second neighbor command illustrates specification of an internal neighbor (with the same autonomous system number) at address 131.108.234.2; and the last neighbor command specifies a neighbor on a different network.

Syntax Description

Default

No route maps are applied to a peer.

Command Mode

Router configuration

Usage Guidelines

If an outbound route map is specified, it is proper behavior to only advertise routes that match at least one section of the route map.

Examples

In the following example, route map "internal-map" is applied to incoming route from 198.92.70.24:

Syntax Description

Default

No COMMUNITIES attribute is sent to any neighbor.

Command Mode

Router configuration

Examples

In the following example, the router belongs to autonomous system 109 and is configured to send the communities attribute to its neighbor at IP address 198.92.70.23:

Related Commands

ip community-list
match community-list
set community

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

Using this third-party mechanism, EGP tells its peer that another communication server (the third party) on the shared network is the appropriate communication server for some set of destinations. If updates mentioning third-party communication servers are desired, use this command.

All networks reachable through the third-party communication server will be listed in the EGP updates as reachable by the communication server. The optional internal and external keywords indicate whether the third-party communication server should be listed in the internal or external section of the EGP update. Normally, all networks are mentioned in the internal section.

This command can be used multiple times to specify additional third-party communication servers.

Examples

In the following example, routes learned from communication server 131.108.6.99 will be advertised to 131.108.6.5 as third-party internal routes:

In the following example, routes learned from 131.108.6.100 will be advertised to 131.108.6.5 as third-party external routes:

Syntax Description

Default

Best-local-address

Command Mode

Router configuration

Usage Guidelines

This feature works in conjunction with the Loopback interface feature described in the "Configuring Interfaces" chapter of the Access and Communication Servers Configuration Guide.

Example

In the following example, BGP TCP connections for the specified neighbor will be sourced with Loopback interface's IP address rather than the best-local-address:

Syntax Description

Default

Version 4

Command Mode

Router configuration

Usage Guidelines

Entering this command disables dynamic version negotiation.

Our implementation of BGP supports Versions 2, 3, and 4 of BGP. If the neighbor does not accept default version 4, dynamic version negotiation is implemented to negotiate down to version 2.

Example

The following example locks down to Version 4 of the BGP protocol:

Syntax Description

Default

Routes learned through another BGP peer have a default weight of 0 and routes sourced by the local communication server have a default weight of 32768.

Command Mode

Router configuration

Usage Guidelines

All routes learned from this neighbor will have the assigned weight initially. The route with the highest weight will be chosen as the preferred route when multiple routes are available to a particular network.

The weights assigned with the match as-path and set weight route-map commands override the weights assigned using the neighbor weight and neighbor filter-list commands.

Example

The following example sets the weight of all routes learned via 151.23.12.1 to 50:

Related Commands

neighbor distribute-list
neighbor filter-list

Syntax Description

Default

No networks are specified.

Command Mode

Router configuration

Usage Guidelines

These types of networks can be learned from connected routes, dynamic routing, and from static route sources.

A maximum of 200 network commands may be specified for a single BGP process.

Example

The following example sets up network 131.108.1.27 to be included in the communication server's BGP updates:

Related Commands

network backdoor
network mask
network weight
router bgp

Syntax Description

Default

No networks are specified.

Command Mode

Router configuration

Usage Guidelines

The networks to be advertised to the EGP peers of an EGP routing process are advertised with a distance of zero. The restrictions on the network you specify are that it must appear in the routing table, and the network number must not contain any subnet information. The network can be connected, statically configured, or redistributed into EGP from other routing protocols. Multiple commands can be used to specify additional networks.

Example

The following example illustrates a typical configuration for an EGP communication server process. The communication server is in autonomous system 109 and is peering with communication servers in autonomous system 164. It will advertise the networks 131.108.0.0 and 192.31.7.0 to the communication server in autonomous system 164, 10.2.0.2. The information sent and received from peer communication servers can be filtered in various ways, including blocking information from certain communication servers and suppressing the advertisement of specific routes.

Related Command

router egp

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

The network number must not contain any subnet information. You can specify multiple network commands.

IP Enhanced IGRP sends updates to the interfaces in the specified network(s). Also, if you do not specify an interface's network, it will not be advertised in any IP Enhanced IGRP updates.

Example

The following example configures a communication server for IP Enhanced IGRP and assigns autonomous system number 109. The network commands indicate the networks directly connected to the communication server.

Related Command

router eigrp

Syntax Description

Default

No networks are specified.

Command Mode

Router configuration

Usage Guidelines

The network number specified must not contain any subnet information. You can specify multiple network commands.

IGRP sends updates to the interfaces in the specified network(s). Also, if an interface's network is not specified, it will not be advertised in any IGRP update.

Example

The following example configures a communication server for IGRP and assigns autonomous system 109. The network commands indicate the networks directly connected to the communication server.

Related Command

router igrp

Syntax Description

Default

No networks are specified.

Command Mode

Router configuration

Usage Guidelines

The network number specified must not contain any subnet information. You can specify multiple network commands. RIP routing updates will be sent and received only through interfaces on this network.

RIP sends updates to the interfaces in the specified networks. Also, if an interface's network is not specified, it will not be advertised in any RIP update.

Example

The following example defines RIP as the routing protocol to be used on all interfaces connected to networks 128.99.0.0 and 192.31.7.0:

Related Command

router rip

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

The address and wildcard-mask arguments together allow you to define one or multiple interfaces to be associated with a specific OSPF area using a single command. Using the wildcard-mask allows you to define one or multiple interfaces to be associated with a specific OSPF area using a single command. If you intend to associate areas with IP subnets, you can specify a subnet address as the area-id.

The communication server sequentially evaluates the address/wildcard-mask pair for each interface as follows:

1. The wildcard-mask is logically ORed with the interface IP address.

2. The wildcard-mask is logically ORed with address in the network command.

3. The communication server compares the two resulting values.

4. If they match, OSPF is enabled on the associated interface and this interface is attached to the OSPF area specified.

Example

In the following partial example, OSPF routing process 109 is initialized, and four OSPF areas are defined: 10.9.50.0, 2, 3, and 0. Areas 10.9.50.0, 2, and 3 mask specific address ranges, while Area 0 enables OSPF for all other networks.

Related Command

router ospf

Syntax Description

Default

No network is advertised.

Command Mode

Router configuration

Usage Guidelines

A backdoor network is treated as a local network, except that it is not advertised.

Example

The following example configures network 131.108.0.0 as a local network and network 192.31.7.0 as a backdoor network:

Syntax Description

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

The offset value is added to the routing metric. An offset-list with an interface type and interface number is considered extended and takes precedence over an offset-list that is not extended. Therefore, if an entry passes the extended offset-list and the normal offset-list, the extended offset-list's offset is added to the metric.

Examples

The following example applies an offset of 10 to the communication server's delay component for all outgoing metrics:

In the following example, the communication server applies the same offset in the previous example only to access list 121:

In the following example of an extended offset-list, the communication server applies the offset of 10 to routes learned from Ethernet interface 0:

Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Router configuration

Usage Guidelines

In Cisco IOS Release 10.2 and earlier, OSPF assigns default OSPF metrics to interfaces regardless of the interface bandwidth. It gives both 64K and T1 links the same metric (1562), and thus requires an explicit ip ospf cost command in order to take advantage of the faster link.

In Cisco IOS Release 10.3, by default OSPF will calculate the OSPF metric for an interface according to the bandwidth of the interface. For example, a 64K link will get a metric of 1562, while a T1 link will have a metric of 64.

The OSPF metric is calculated as metric-scale / bandwidth, with metric-scale equal to 10⁸ by default, which gives FDDI, for example, a metric of 1.

Example

The following example causes a fixed default metric assignment, regardless of interface bandwidth:

Related Command

ip ospf cost

Syntax Description

Default

Routing updates are sent on the interface.

Command Mode

Router configuration

Usage Guidelines

If you disable the sending of routing updates on an interface, the particular subnet will continue to be advertised to other interfaces, and updates from other communication servers on that interface continue to be received and processed.

IP Enhanced IGRP is disabled on an interface that is configured as passive although it advertises the route.

For OSPF, OSPF routing information is neither sent nor received through the specified communication server interface. The specified interface address appears as a stub network in the OSPF domain.

Example

The following example sends IGRP updates to all interfaces on network 131.108.0.0 except Ethernet interface 1:

Syntax Description

Defaults

Route redistribution is disabled.

protocol—No source protocol is defined.
process-id—No process ID is defined.
metric metric-value—0
metric-type type-value—Type 2 external route
match internal | external—internal
external type-value—internal
tag tag-value—If no value is specified, the remote autonomous system number is used for routes
     from BGP and EGP; for other protocols, the default is 0.

route-map map-tag—If the route-map argument is not entered, all routes are redistributed; if no
     map-tag value is entered, no routes are imported.
weight weight—No network weight is defined.
subnets—No subnets are defined.

Command Mode

Router configuration

Usage Guidelines

Changing or disabling any keyword will not affect the state of other keywords.

A communication server receiving a link-state protocol (LSP) with an internal metric will consider the cost of the route from itself to the redistributing communication server plus the advertised cost to reach the destination. An external metric only considers the advertised metric to reach the destination.

Routes learned from IP routing protocols can be redistributed at level-1 into an attached area or at level-2. The keyword level-1-2 allows both in a single command.

Redistributed routing information should always be filtered by the distribute-list out router configuration command. This ensures that only those routes intended by the administrator are passed along to the receiving routing protocol.

Whenever you use the redistribute or the default-information router configuration commands to redistribute routes into an OSPF routing domain, a communication server acting as a communication server automatically becomes an Autonomous System Boundary Router (ASBR). However, an ASBR does not, by default, generate a default route into the OSPF routing domain.

When routes are redistributed between OSPF processes, no OSPF metrics are preserved.

The only connected routes affected by this redistribute command are the routes not specified by the network command.

You cannot use the default-metric command to affect the metric used to advertise connected routes.

Default redistribution of IGPs or EGP into BGP is not allowed unless default-information originate is specified.

When routes are redistributed into OSPF and no metric is specified in the metric keyword, the default metric that OSPF uses is 20 for routes from all protocols except BGP route, which gets a metric of 1.

Examples

The following are examples of the various configurations you would use to redistribute one routing protocol into another routing protocol.

The following example configuration causes OSPF routes to be redistributed into a BGP domain:

The following example configuration causes IGRP routes to be redistributed into an OSPF domain:

The following example causes the specified IGRP process routes to be redistributed into an OSPF domain. The IGRP-derived metric will be remapped to 100 and RIP routes to 200.

In the following example, BGP routes are configured to be redistributed into IS-IS. The link-state cost is specified as 5, and the metric type will be set to external, indicating that it has lower priority than internal metrics.

Related Commands

default-information allowed
distribute-list out
route-map
show route-map

Syntax Description

Default

No default available.

Command Mode

Global configuration

Usage Guidelines

Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.

Use route maps when you wish to have detailed control over how routes are redistributed between routing processes. The destination routing protocol is the one you specify with the router global configuration command. The source routing protocol is the one you specify with the redistribute router configuration command. See the following example as an illustration of how route maps are configured.

Examples

The following example redistributes all OSPF routes into IGRP:

The following example redistributes RIP routes with a hop count equal to 1 into OSPF. These routes will be redistributed into OSPF as external link state advertisements with a metric of 5, metric type of Type 1 and a tag equal to 1.

Related Commands

Syntax Description

Default

No BGP routing process is enabled by default.

Command Mode

Global configuration

Usage Guidelines

This command allows you to set up a distributed routing core that automatically guarantees the loop-free exchange of routing information between autonomous systems.

Example

The following example configures a BGP process for autonomous system 120:

Related Commands

neighbor
network (BGP)
timers bgp

Syntax Description

Default

No EGP routing process is defined.

Command Mode

Global configuration

Usage Guidelines

You must specify the autonomous system number before starting EGP. The local autonomous system number will be included in EGP messages sent by the communication server. The software does not insist that the actual remote autonomous system number match the configured autonomous system numbers. The output from the debug ip-egp EXEC command will advise of any discrepancies.

Example

The following example assigns a communication server to autonomous system 109 and is peering with communication servers in autonomous system 164:

Related Commands

autonomous-system
neighbor
network (EGP)
timers egp

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Global configuration

Usage Guidelines

Core gateways are central clearinghouses of routing information. Only one core gateway process can be configured in a communication server.

The router egp 0 global configuration command allows a specific communication server to have an EGP process that will enable it to act as a peer with any reachable autonomous system and information is exchanged freely between autonomous systems.

Normally, an EGP process expects to communicate with neighbors from a single autonomous system. Because all neighbors are in the same autonomous system, the EGP process assumes that these neighbors all have consistent internal information. Therefore, if the EGP process is informed about a route from one of its neighbors, it will not send it out to other neighbors.

With core EGP, the assumption is that all neighbors are from different autonomous systems, and all have inconsistent information. In this case, the EGP process distributes routes from one neighbor to all others (but not back to the originator). This allows the EGP process to be a central clearinghouse for information.

Example

The following example illustrates how an EGP core gateway can be configured:

Related Commands

neighbor any
neighbor any third-party

Syntax Description

Default

Disabled

Command Mode

Global configuration

Example

The following example shows how to configure an IP Enhanced IGRP routing process and assign autonomous system number 109:

Related Command

network

Syntax Description

Default

No IGRP routing process is defined.

Command Mode

Global configuration

Usage Guidelines

You are not required to have a registered autonomous system number to use IGRP. If you do not have a registered number, you can create your own. However, if you do have a registered number, we recommends that you use it to identify the IGRP process.

Example

The following example shows how to configure an IGRP routing process and assign autonomous system 109:

Related Command

network (IGRP)

Syntax Description

Default

No OSPF routing process is defined.

Command Mode

Global configuration

Usage Guidelines

You can specify multiple OSPF routing processes in each communication server.

Example

The following example shows how to configure an OSPF routing process and assign a process ID of 109:

Related Command

network (OSPF)

Syntax Description

This command has no arguments or keywords.

Default

No RIP routing process is defined.

Command Mode

Global configuration

Example

The following example shows how to begin the RIP routing process:

Related Command

network (RIP)