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

Neighbor Command on CISCO Router/Switch 1Looking 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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