RE: OSPF Learned Routes

>R2 also peers up with R3 via OSPF only.
You mean NEIGHBORS, but we get you...

You LSA passing assumption is correct... remember each router has one or more local RIB's (OSPF, iBGP, etc) and a single FIB (ok 1 fib per VRF :)

Within a single AREA OSPF maintains a completely synchronized LSA database. So while R2 may LOCALLY prefer IBGP routes to the same destinations as OSPF, R3 will never know this from how its generating its FIB (routing table).

Quite common behavior... of course in a production network you probably would never want this, as R2 could route traffic is a sub-optimal direction (i.e. to another farther ibgp path, than the OSPF internal path)

-Joe

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Joe Astorino
Sent: Tuesday, May 05, 2009 10:03 PM
To: CCIE Groupstudy
Subject: OSPF Learned Routes

I have a quick question on something I never particuarly noticed before.

Assume you have R1, and R2. They peer via iBGP as well as OSPF. R2 also peers up with R3 via OSPF only. On R2 you have set the AD for iBGP routes to 50 so they are preferred over OSPF.

However, even though you have routes on R2 learned via R1 through iBGP in the routing table with AD 50, R3 still has the routes learned from R2 as OSPF routes.

This sort of confused me because they are not OSPF routes on R2 but are still being advertised to R3 in OSPF. The only thing I am thinking is that even though they are not OSPF routes on R2, it still passes the LSAs to R3 and R3 still runs SPF and puts the routes in the routing table.

Can anybody verify what is happening there?

"He not busy being born is busy dying" -- Dylan

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Received on Tue May 05 2009 - 22:14:53 ART