Default Passive Interface

2017-11-03 09:05:04

Problem

You want to disable RIP on all of a router's interfaces, except for a few that you specify.

Solution

You can disable the sending of RIP updates on all interfaces with the passive-interface default command:

Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#router rip Router1(config-router)#passive-interface default Router1(config-router)#no passive-interface FastEthernet0/0.1 Router1(config-router)#network 172.22.0.0 Router1(config-router)#network 172.25.0.0 Router1(config-router)#network 192.168.1.0 Router1(config-router)#exit Router1(config)#end Router1#

Discussion

The RIP network command has two functions. The first function tells RIP which routing prefixes to distribute. The second turns on RIP updates on all interfaces whose addresses are included in the range specified by the network command. Sometimes you want to send routing information for a subnet, but you don't want to actually run RIP on the corresponding interface, as we described in Recipe 6.6. If there are interfaces that you don't want to send RIP updates, you can individually disable them by using the passive-interface command, as we did in Recipe 6.6. But sometimes you don't want interfaces to take part in RIP unless you explicitly enable them, even if they happen to have addresses that are covered by a network command.

This is mostly used as a convenience on routers that have a lot of interfaces, particularly when only a few of those interfaces will be running RIP. You use this feature by entering the passive-interface default command, and then explicitly re-enabling RIP with the no passive-interface command on those interfaces where you do want it:

Router1(config)#router rip Router1(config-router)#passive-interface default Router1(config-router)#no passive-interface FastEthernet0/0.1

You can then use as many network commands as you like, but RIP updates will only be sent on the interfaces that you explicitly list.

Using the passive-interface default command can save time, while also making it simpler to troubleshoot problems because you don't have to carefully count all of the interfaces to figure out which ones should be running the routing protocol:

Router1#show ip protocols Routing Protocol is "rip" Sending updates every 30 seconds, next due in 13 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Triggered RIP Key-chain FastEthernet0/0.1 1 1 2 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 172.22.0.0 172.25.0.0 Passive Interface(s): FastEthernet0/1 Serial0/0.2 Routing Information Sources: Gateway Distance Last Update 172.25.1.7 120 00:00:09 172.25.2.2 120 00:00:01 Distance: (default is 120) Router1#

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