What is Passive-Interface Command Behavior in RIP, EIGRP & OSPF?
Routing protocols specify how routers talk to each other to exchange information about routes within the same system. This communication happens by sending all or a portion of routing tables in routing-update messages to their neighbors.
Passive-Interface Command Behavior in RIP
While configuring a router, if we want to prevent an interface from participating in RIP, we can use the passive-interface command. This will disable sending multicast updates via that specific interface. But this will allow listening to incoming updates from other RIP-speaking neighbors. Thus interface will still be able to learn new routes.
Passive-Interface Command Behavior in EIGRP
In the case of EIGRP, passive-interface command prevents directly connected routers from establishing EIGRP neighbor relationships. Now they can’t become neighbors, so they will never exchange routing information. In RIP, the passive-interface command still allows acceptance of new routes, it just won’t send them. But in EIGRP, passive-interface command will result in neither sending nor receiving any routing information.
Passive-Interface Command Behavior in OSPF
In the case of OSPF, adjacencies are formed to exchange routing information. An OSPF-enabled router sends Hello packets out all OSPF-enabled interfaces to determine whether neighbors are present on those links. If a neighbor is present then the OSPF-enabled router attempts to establish neighbor adjacency with that neighbor. If we want to prevent some or all of the router’s interfaces from taking part in OSPF, we can use the passive-interface command. The passive-interface command effectively disables OSPF on an interface by preventing it from forming OSPF adjacencies.
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