GRE over MPLS

[bssmith10]

We are getting ready to migrate our WAN backbone from frame relay to MPLS with AT&T. We have multiple internet entry points thorugh our network and have selectively routed traffic to the various internet connections through configured defaul-routes. We are being told by AT&T that to continue this routing we will need to use GRE Tunnels. My question is if location A has normal routing to location B, which has one of the internet connections, through the MPLS cloud via BGP, and I configure a GRE tunnel between the two sites, and configure default routing from site A to site B through the tunnel, how is the routing done at site B. I only want internet based traffic from site A to site B to use the tunnel, and all other traffic between the two sites to use the normal links through the MPLS cloud.

[alfredshum]

On router B, you must have a default route towards the Internet, and use BGP to advertise the internal networks to the PER in MPLS and the PER will in turn advertise these networks to router A.

[bssmith10]

The problem is that once the PER advertises the default route, site C will recieve that route, and site C needs to get to the internet through site D. Hence the need for the GRE Tunnels. I need internal traffic between network A and network B to use the normal MPLS routes, but internet traffic from A through B to the internet needs to use the Tunnel. How do I keep the return internet traffic from site B to site A on the tunnel, and traffic between the internal networks off the tunnel? Route Maps?

[tekha]

Sounds to me like you wan't 2 seperate MPLS.

If you have one MPLS called vrf #1 and another called vrf #2.

Then put router A and B in vrf #1, and router C and D in vrf #2.

Then get AT&T to import/export all routes between the two vrf's, except the default routes. That would give you what you need, without having to do GRE tunnels.

[bssmith10]

I am not familiar with vrf. Can you point me to a link or white paper that discusses this?

[tekha]

Well you don't need to know anything about it, because it would all be done in AT&T's equipment.

But here is a link on configuring MPLS.

http://www.cisco.com/en/US/tech/tk436/tk428/technologies_configuration_example09186a00800a6c11.shtml

[alfredshum]

"use BGP to advertise the internal networks to the PER"

I didn't say that you should advertise your default route into the MPLS network. Just advertise the LAN subnets, WAN subnets...etc. Not 0.0.0.0/0.

If you use GRE tunnel, you'll have to manually install a static default route which by default will override any dynamically learnt default route if any.

[bssmith10]

Thanks, I like this approach, and actually think I can do it without using GRE tunnels, which will follow the KISS method.