Sunday, November 16, 2008

MPLS VPNs with Extranets Complete

I was pretty surprised I got this one right the first time. It's simply a matter of getting the route target imports and exports correct.

I think I'm still a little fuzzy on the transition from an IP address to a route descriptor to a route-target, and how they all interoperate with routing protocols and redistribution.

This lab did help to tie it together somewhat. I suppose my understanding is that it goes something like this:

When an interface is setup for vrf forwarding, it is no longer part of the global routing table. Instead, the router performs a lookup to get more details about the vrf that the interface is an instance of. It goes to the vrf configuration and finds the route descriptor, which is uses to relate this interface to IGPs and ipv4 BGP. Then, it sends out a BGP vpnv4 route for each export target. These export targets get flooded throughout the BGP vpnv4 peers, which should encompass all PE routers. Finally, with these vpnv4 routes flooded, the import route-target is used to load the remote vpnv4 routes into the particular vrf routing table.

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