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Multihomed EIGRP Sites in MPLS VPN Network

Deploying EIGRP as the PE-CE routing protocol in MPLS VPN networks is easy if all sites have a single PE-CE link and there are no backdoor links between the sites. Real life is never as simple as that; you have to cope with various (sometimes undocumented) network topologies. Even that would be manageable if the customer networks would have a clean addressing scheme that would allow good summarization (that happens once in a blue moon) or if the MPLS VPN core could announce the default route into the EIGRP sites (wishful thinking; the customer probably has one or more Internet exit points).

In the end, you’re left with two-way route redistribution between core MP-BGP and edge EIGRP, resulting in nightmarish scenarios (probably a good half of the blog posts of the CCIE candidates talk about redistribution horrors). Fortunately, Cisco implemented two extra features supporting EIGRP-to-MP-BGP redistribution: BGP cost community and BGP Site-of-Origin. I described them both in an article that is long gone; its shadow has been preserved on archive.org.

Would you like me to migrate that article to ipSpace.net? Send me a message and I just might do it...

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