For EIGRP,the passive-interface command will stop sending the Hello packets. So they will not come to be neighbors. We sometime don't want the router to do things like that on the loopback interface. We sometime want to make sure that the particular interfaces are running EIGRP. We sometime use big subnets in the network command within the EIGRP process. The network command may includes many interfaces to run it but we don't want all of them.
Just to re-word what Toshi rightly point out, the purpose is to prevent the interface from participating in the route exchange process. Sometimes you dont want an interface is have a neighbor or an adjacency.
Though the passive-interface command stops sending hellos on the interface and thereby prevents forming a neighbor relationship between 2 EIGRP routers, it will still advertise the subnet of that interface within the EIGRP domain, so you will see that subnet in the IP routing tables of the EIGRP routers.
So the use is:
When you don't want the neighbor relationship to form (for example certain ISP connections), but you still want all EIGRP routers (or users) to reach that subnet and therefore you want to advertise it.
If you don't want to form a neighbor relationship and don't want reachability to that subnet either, then you will need to carefully select the numbers and the wildcard mask after the "network" command under the EIGRP routing process, so that interface will not be selected at all under the EIGRP process.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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