apparent OSPF woes

fatroadie · ‎06-17-2008

Just migrated our DC from EIGRP to OSPF last weekend. We are having apparent issues when anything in the DC has a route change, then the entire OSPF route table refreshes. Is this typical behavior?

Our environment running OSPF in our DC (19 devices) is mostly 6509's with a handful of 7507/7513s. There are 2 WAN 75xx that are doing bidirectional redistribution into/out of EIGRP. Everything is in area 0.

Here's configs of the redistribution piece:

Primary WAN rtr:

router eigrp 1

redistribute ospf 1 metric 100000 20070 250 255 1500

network 10.0.0.0

network x.x.x.x 0.0.0.3

no auto-summary

!

router ospf 1

log-adjacency-changes

area 0 authentication message-digest

redistribute eigrp 1 metric 10 subnets

network 10.0.0.0 0.255.255.255 area 0

distance ospf intra-area 10 inter-area 10 external 150

backup WAN rtr:

router eigrp 1

redistribute ospf 1 metric 50000 40000 250 255 1500

network 10.0.0.0

network x.x.x.x 0.0.0.3

no auto-summary

!

router ospf 1

log-adjacency-changes

area 0 authentication message-digest

redistribute eigrp 1 metric 90 subnets

network 10.0.0.0 0.255.255.255 area 0

distance ospf intra-area 10 inter-area 10 external 150

As you can see, we have adjusted metrics on the backup rtr so that routes are preferred through the primary rtr. Additionally, our service provider is running SOO to help with routing loops.

ralphcarter · ‎06-17-2008

When you redistribute routes into OSPF, that particular router becomes an ASBR. You can summarize these redistributed routes into OSPF on ASBRs and if a particular route (one of the redistributed and summarized) goes down, it will not affect the OSPF neighbors.

# router ospf 1

# summary-address x.x.x.x 255.255.255.0

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fatroadie · ‎06-18-2008

Ok, so this is my first time running OSPF! I've been told that when an intra-area route changes, the SPF algorithm runs and does a full refresh of the routes. As long as the traffic itself isn't affected, that's ok. I think we'll just need to break our area 0 up so that when area 0 actually does show a route refresh, that something happened that warrants investigation.

michaelchoo · ‎06-18-2008

Worthy of note here is OSPF is a link-state protocol within a given area only! Behavior of inter-area communications is very much like distance vector. Hence, it's important to summarize on ABR and/or ASBR when possible.

It might be worthwhile to create an NSSA area for the routers doing redistribution from EIGRP, and make sure that those routers summarize the redistributed routes into OSPF.