Neighbor Command on CISCO Router/Switch

Command

Neighbor

Use

This command tells RIP to communicate with unicast updates to a specific neighbor. This is usually used with the passive-interface default command to prevent all other RIP communication.

Syntax

Router(config-router)#neighbor <ip address>

Example

In this example, we will configure R4 to send its updates to R3 using unicast

Looking at the debug output for RIP we see that updates are currently being sent to RIP’s multicast address 224.0.0.9

R4(config-router)#do debug ip rip
RIP protocol debugging is on
R4(config-router)#
*Mar 1 00:15:05.811: RIP: sending v2 update to 224.0.0.9 via Serial0/0 (10.4.4.4)
*Mar 1 00:15:05.815: RIP: build update entries
*Mar 1 00:15:05.815: 1.1.1.1/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:15:05.819: 1.2.2.2/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:15:05.819: 1.3.3.3/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:15:05.823: 10.1.1.0/24 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:15:05.823: 10.4.4.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 1 00:15:05.823: 11.11.11.11/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:15:05.823: 111.111.111.111/32 via 10.4.4.1, metric 2, tag 0

Next we configure passive-interface default to block all RIP updates and configure R4 to sent updates via unicast.

R4(config)#router rip
R4(config-router)#passive-interface default
R4(config-router)#neighbor 10.4.4.3

Notice that updates are now being sent directly to R3.

R4(config-router)#do debug ip rip
RIP protocol debugging is on

*Mar 1 00:11:49.371: RIP: sending v2 update to 10.4.4.3 via Serial0/0 (10.4.4.4)
*Mar 1 00:11:49.375: RIP: build update entries
*Mar 1 00:11:49.375: 1.1.1.1/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:11:49.379: 1.2.2.2/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:11:49.379: 1.3.3.3/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:11:49.383: 10.1.1.0/24 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:11:49.383: 10.4.4.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 1 00:11:49.383: 11.11.11.11/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:11:49.383: 111.111.111.111/32 via 10.4.4.1, metric 2, tag 0
*Mar 1 00:11:49.383: RIP: sending v2 update to 10.4.4.1 via Serial0/0 (10.4.4.4)

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