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Why do we configure loopback IP address in router RIP and router OSPF configuration ? What is the significance of configuring it ?

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closed as not constructive by EightBitTony, Alex, Dave M, Lucas Kauffman, Ward Jan 24 '13 at 15:03

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What's the real world problem you're trying to solve here? Please read this serverfault.com/faq#dontask which explains why I'm asking. –  EightBitTony Jan 24 '13 at 12:30
    
I've never heard of doing that. Where are you getting that information and on what router platform are you doing this? –  joeqwerty Jan 24 '13 at 13:30

1 Answer 1

This is a preferred design pattern on Cisco routers:

Configuring OSPF: Configuring Your OSPF Network Type

OSPF uses the largest IP address configured on the interfaces as its router ID. If the interface associated with this IP address is ever brought down, or if the address is removed, the OSPF process must recalculate a new router ID and resend all its routing information out its interfaces.

If a loopback interface is configured with an IP address, the Cisco IOS software will use this IP address as its router ID, even if other interfaces have larger IP addresses. Because loopback interfaces never go down, greater stability in the routing table is achieved.

OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address among all loopback interfaces. If no loopback interfaces are present, the highest IP address in the router is chosen. You cannot tell OSPF to use any particular interface.

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