Monday, December 29, 2008

IE Vol 1: Carrier Supporting Carrier - IP Only

In this lab, the goal is to segment one AS (something like a tier-2 carrier) with another AS (a tier-1 carrier). It's quite interesting how this ends up working out. The Tier-1 carrier becomes the P network, and the tier-2 carrier becomes the C network. iBGP relationships can still be formed by CE routers across the P network, since as far as the CE routers are concerned, the routes are all being learned via OSPF. The entire separate AS is completely transparent to the C network.

There really wasn't anything particularly challenging about this lab, there was just a lot going on. It's definitely required to build each piece step by step and verify along the way. A simple missing mpls adjacency, ospf neighbor, or bgp next-hop-self missing could make troubleshooting really difficult.

The mpls verification was quite interesting. On the PE routers, a separate MPLS adjancency is actually formed inside of the vrf. To check this, the commands sh mpls ldp neigh vrf VPN_A and sh mpls for vrf VPN_A are required.

Aside from that, I had to go back and do a couple of redistribute connected's into bgp. This was required so that I could ping from the outgoing interface rather than the loopback of the true customer routers.

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