Passive Interfaces

For security reasons and to reduce unnecessary traffic, RIP updates should not be propagated into the OSPF domain. You can disable sending updates with the passive-interface interface_type interface_number router configuration command

Making an interface in RIP passive only disables updates from being sent through RIP. It does not affect routes being received through it.

Putting a RIPv2 interface in passive mode saves the router from sending multicast RIP packets out an interface that has no neighbors.

To verify RIPv2 send advertisements out loopback interfaces: monitor the output of the debug ip rip command to verify your answer. Configure all loopbacks from which RIPv2 is sending advertisements in passive state with the passive-interface command.

When running RIPv2, implement passive interfaces as a common practice to save CPU processor cycles and bandwidth on interfaces that do not have multicast RIPv2 neighbors.

Passive interfaces save CPU cycles, router memory, and link bandwidth by preventing broadcast and multicast routing updates on interfaces that have no neighbors. In link-state protocols, adjacencies must be formed before routers exchange routing information. The passive-interface command in OSPF configuration mode prevents an interface from sending or processing OSPF packets on that interface.

You can use the passive-interface command to control the advertisement of routing information.
The command enables the suppression of routing updates over some interfaces while it allows
updates to be exchanged normally over other interfaces.
With most routing protocols, the passive-interface command restricts outgoing advertisements
only. However, when used with Enhanced Interior Gateway Routing Protocol (EIGRP), the effect is
slightly different. With EIGRP running on a network, the passive-interface command stops both
outgoing and incoming routing updates, since the effect of the command causes the router to stop
sending and receiving hello packets over an interface.

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