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Redistribution & Summarisation

I have a strange problem with advertising an ip summary route via eigrp. Basically we have two 6509's each with a pair of MSFC's, connected over a single Gig fibre. There is more to the network, but we have isolated it. One pair of MSFC's are redistributing OSPF into EIGRP via a distribute list, the EIGRP then runs across the link to the other pair of MSFC's. We have configured a summary on the outbound interface for EIGRP, summarising the subnets being redistributed from OSPF.

We found that one of the redistributing MSFC's would install the summary into the routing table (next hop Null0) and advertise it to the other pair, whereas the other redistributing MSFC would not install the summary, instead it would learn the EIGRP summary coming from his peer (over the Vlan connecting the 2 chassis together). The only way to stop this is to filter incoming updates to stop the summary being learnt from eachother, all then works ok.

Why does this happen? The summary should have an admin distance of 5 (by default) and should win over the EIGRP (90) route being heard from the peer. Is this some kind of weird split horizon issue?


Re: Redistribution & Summarisation

Often times complex troubleshooting issues are best addressed in an interactive session with one of our trained technical assistance engineers. While other forum users may be able to help, it’s often difficult to do so for this type of issue.

To utilize the resources at our Technical Assistance Center, please visit and to open a case with one of our TAC engineers, visit

If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.