ndp(1M)

NAME

ndp — IPv6 Neighbor Discovery cache display and control

SYNOPSIS

ndp host

ndp [-i interface] [-n] -a

ndp [-i interface] [-n] -A interval

ndp [-i interface] [-q] -d host

ndp [-i interface] [-nq] -F

ndp [-i interface] -p

ndp [-i interface] [-q] -P

ndp -s interface host hw_addr [pub]

ndp -f filename

DESCRIPTION

The ndp command displays and modifies the IPv6 Neighbor Discovery cache as specified in the IPv6 Neighbor Discovery (ND) protocol.

Options

ndp recognizes the following options and arguments:

host

Display the current Neighbor Discovery cache entries for the host specified by host, which is either a name present in the hostname database (see hosts(4)), or an IPv6 address expressed in colon notation (see inet6(3N)).

-i interface

Select the Neighbor Discovery cache entries for the specified interface. There is no distinction between primary and secondary interfaces. Therefore, specifying -i lan1:1 is the same as specifying -i lan1.

-n

Display host addresses in IPv6 colon notation. If this option is not specified, ndp attempts to display host addresses symbolically first, and falls back to displaying the host addresses in IPv6 colon notation if that failed.

-a

Display all Neighbor Discovery cache entries.

-A interval

Continuously display all Neighbor Discovery cache entries, updated at each interval , measured in seconds.

-d host

Deletes Neighbor Discovery cache entries with IP addresses that are not associated with local interfaces for the host specified by host.

-F

Flushes all Neighbor Discovery cache entries with IP addresses that are not associated with local interfaces. These are entries with the L flag set.

-q

(Quiet) Do not write anything to standard output. This option only applies to -d, -F, and -P options.

-p

Display the prefix list in the Neighbor Discovery cache table. The prefix list defines a set of IP address ranges that the host can reach. The prefix flags are L for on-link, and A for autonomous. The on-link flag indicates that addresses with that prefix can be reached directly without going through a router. The autonomous flag indicates that the prefix came from stateless autoconfiguration.

-P

Flushes all autoconfigured addresses learned from prefixes advertised by the Router Advertisement Messages.

-s interface host hw_addr [pub]

Create a Neighbor Discovery cache entry for the interface specified by interface, the host specified by host, and the hardware address (link-layer address) specified by hw_addr. The hw_addr is specified as xx:xx:xx: xx:xx:xx, where each x is a hexadecimal digit. If pub is specified, the entry is published, which means that this system will respond to Neighbor Solicitation for the specified "host" even though the host address is not its own.

-f filename

Create Neighbor Discovery cache entries from the specifications found in the file specified by filename. Each entry in this file specifies the interface, host, hw_addr, and optionally the pub flag. For example, the content of this file can be:

lan0 nodea 1:2:3:4:5:6

lan1 nodeb 2:3:4:5:6:7 pub

The use of -d, -F, -P, -s, and -f options requires root privileges.

A Neighbor Discovery cache entry includes the following fields:

host (neighbor's host name or IP address)
hardware address (link layer address) of host
interface name
state
flags

The state of an entry can be INCOMPLETE, REACHABLE, STALE, DELAY, or PROBE.

An entry is in an INCOMPLETE state if address resolution is in progress and the hardware address of the neighbor has not been determined.
An entry is in a REACHABLE state if the neighbor is known to have been reachable recently.
An entry is in a STALE state if the neighbor is no longer known to be reachable. However, no attempt has been made to verify its reachability because no traffic has been sent to this neighbor.
An entry is in a DELAY state if the neighbor is no longer known to be reachable, and traffic has recently been sent to the neighbor.
An entry is in a PROBE state if the neighbor is no longer known to be reachable, and unicast Neighbor Solicitation probes have been sent to verify reachability.

The flags can be D (deprecated), L (local), or P (published). A deprecated address can be used for receiving packets, but it should not be used for sending packets because its validity is expected to expire soon. The local flag indicates that this Neighbor Discovery cache entry corresponds to an interface on this host. The published flag indicates that the host will respond to Neighbor Solicitations on this IPv6 address.

DIAGNOSTICS

ndp returns a non-zero value to indicate errors. A zero return value indicates success.

EXAMPLES

The following netstat output shows the local interfaces and the IP addresses assigned to them.

# netstat -inf inet6

Name      Mtu Address/Prefix                       Ipkts    Opkts
lan1     1500 fe80::210:83ff:fef7:3a21/10            982      759
lan1:1   1500 fec0::9:210:83ff:fef7:3a21/64            0        0
lan3     1500 fe80::210:83ff:fef7:7a9d/10              0        0
lo0      4136 ::1/128                                 57       57

To display the entire Neighbor Discovery cache:

# ndp -a -n

Destination                Physical Address  Interface State     Flags
fe80::202:fdff:fe36:8720   0:2:fd:36:87:20   lan1      STALE     -
fec0::9:210:83ff:fef7:3a21 0:10:83:f7:3a:21  lan1:1    REACHABLE LP
fe80::210:83ff:fef7:3a21   0:10:83:f7:3a:21  lan1      REACHABLE LP
fe80::210:83ff:fef7:7a9d   0:10:83:f7:7a:9d  lan3      REACHABLE LP

To show Neighbor Discovery cache entries for a host:

# ndp fe80::210:83ff:fef7:3a21

Destination                Physical Address  Interface State     Flags
fe80::210:83ff:fef7:3a21   0:10:83:f7:3a:21  lan1      REACHABLE LP

To show Neighbor Discovery cache entries for an interface:

# ndp -n -i lan3 -a

Destination                Physical Address  Interface State     Flags
fe80::210:83ff:fef7:7a9d   0:10:83:f7:7a:9d  lan3      REACHABLE LP

To delete a Neighbor Discovery cache entries for a host and an interface:

# ndp -i lan1 -d fe80::202:fdff:fe36:8720

fe80::202:fdff:fe36:8720 (fe80::202:fdff:fe36:8720) deleted.

To show the prefix list:

# ndp -p

Prefix List              Interface  Valid     Preferred Flags
 Entries                           Lifetime   Lifetime
 fec0:0:0:9::/64           lan1       167       107      A
 fe80::/10                 lan1       inf       inf      LA
 fe80::/10                 lan3       inf       inf      LA

To add an entry in the Neighbor Discovery cache:

# ndp -s lan3 nodeb 0:1:2:3:4:5

nodeb (2001::1) added.

# ndp -a -n -i lan3

Destination                Physical Address  Interface State     Flags
fe80::210:83ff:fef7:7a9d   0:10:83:f7:7a:9d  lan3      REACHABLE LP
2001::1                    0:1:2:3:4:5       lan3      -         -

To flush all remote entries:

# ndp -F

nodea (fe80::202:fdff:fe36:8720) flushed.
nodeb (2001::1) flushed.

AUTHOR

ndp was developed by HP.

ndp(1M)

Technical documentation

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