loopback interfaces in eigrp

[carl_townshend]

Can anyone tell me, Is it normally good practice to use loopback interfaces when running routing protocol like eigrp ?

thanks

Carl

[Georg Pauwen]

Hello Carl,

here is a little cut & paste from CCO, hope that makes sense:

EIGRP chooses the router ID based on the highest IP address of the loopback interfaces on the router. Since the loopback address never goes down (unless the entire router is down), it is indeed good practice to configure a (unique) loopback address, which then will be used as router ID. Many times, EIGRP will not install routes because of a duplicate router ID problem. EIGRP does not use router ID as extensively as OSPF. EIGRP uses the notion of router ID only on external routes to prevent loops. EIGRP chooses the router ID based on the highest IP address of the loopback interfaces on the router. If the router doesn't have any loopback interfaces, the highest active IP address of all the interfaces is chosen as the router ID for EIGRP.

HTH,

GP

[spremkumar]

Hi

As a best and general practice you can configure the loopback interface with an ip so that it can be assigned as the router-id or taken automatically by the routing process to communicate with the neighbors..

regds

[carl_townshend]

so I guess on the loopback interface we would use ip unnumbered fastethernet0 , so it uses the same ip ?

[ruwhite]

The router ID is only carried in external EIGRP routes (for now) to determine if a router is both redistributing and receiving a route. I wouldn't set the loopback address to a physical interfac address--that defeats the purpose of the loopback interface in this case. In fact, I'd recommend setting the EIGRP router-id command, in later code, to resolve this problem, rather than using the highest loopback address, as in older code. Look at:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800949ab.shtml

Which should help.

:-)

Russ.W