MPLS network design challenge

Unanswered Question
Sep 20th, 2010

Hi,

I have a design issue for which I really like your help.

In a MPLS network there are twoPOP gateway routers (G1,G2) peering with various MPLS VPN Service providers via B2B vrf eBGP peering are in 4 different ASN's. They inturn all peer via VPNv4 eBGP with the Core ASN which comprises of  2 Nos VPNv4 RR's and every site in the ASN haveing 2 P/PE per site. Every P/PE is peering via VPNv4- iBGP with the VPNv4 RR's. The RR's are not in the forwarding path of the traffic.

Every site has 2 Nos CE routers and each CE router does a vrf based ebgp peering with the P/PE's.

The P/PE routers import 2Nos RT exported by the 2 Nos POP G/w routers and inturn selects the best path and pass it to the CE routers.

Now it is seen that the P/PE of all sites is selecting the best path adverstised by G1 instead of  G2 based on the AS PATH length and the shortest path is being adverstised by G1. So till a situation arises that the G1 is down till that time the P/PE's are forwarding the outbound traffic from the CE to G1 even also when the IGP cost is adding up high and when there is a direct link failure from the P/PE site to G1 site.

It therefore makes sense that if the direct physical link form a P/PE site to the site G1 is located goes down ,the P/PE's then should choose  G2 via another path even when G1 is available.

Does these sort of requirements ever come in SP environments from customers ? if so what are the solutions ..

Thanks in advance

Kas

I have this problem too.
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Mahesh Gohil Wed, 09/22/2010 - 03:06

Hi kas,

This type of requirement come to providers and there are few options which provider can implement.

1- Play with local preference along with import map in vrf if requirement is customer specific. I mean if one customer want that G1 should be primary exit point and other customer want G2 as primary exit than he can use import map (which is similar to route-map )

ip vrf ABCD

rd XX

import map ABCD
route-target export XX

route-target import YY

route-map ABCD permit 20
set local-preference >100

2- Or you can play with As-path prepending option if you want to skip selection based on local preference.

it is in provider interest to provide you solution. as there are options of affecting traffic by using communities.

Please provide diagram and some config for complete solution.

Regards

Mahesh

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