When we configure a routing protocol on Cisco IOS Routers, it is important to consider preventing Routing updates sent on interfaces that are not required to (say a LAN where there is no other router in the segment to receive any updates). This ensure we are not passing updates that could cause network issues. Needless to say, the network becomes less chatty and can make life more easy when sniffing or spanning for network troubleshooting.
In Cisco IOS we can globally or selectively prevent interfaces on which we do not want routing updates to be sent. Ideally, it would be better that we do this globally and then selectively allow interfaces that can send routing updates.
To Prevent Routing updates on an Interface
Enter Router config mode (RIP for example)
ciscorouter(config)# router rip
Prevent Routing updates on an Interface (fa0/0 for example)
ciscorouter(config-router)# passive-interface fa0/0
To allow back Routing updates on the interface use the “no” form of the command
ciscorouter(config-router)# no passive-interface fa0/0
To prevent routing updates globally on all interfaces
ciscorouter(config)# router rip ciscorouter(config)# passive-interface default
And now allow selectively allow an interface (say gi1/1/1) to send routing updates
ciscorouter(config)# no passive-interface gi1/1/1/