06-21-2005 02:00 PM - edited 03-03-2019 09:51 AM
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.
06-21-2005 11:36 PM
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.
06-22-2005 06:54 AM
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?
06-22-2005 07:01 AM
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.
06-22-2005 08:15 AM
I am not familiar with vrf. Can you point me to a link or white paper that discusses this?
06-22-2005 12:10 PM
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
06-23-2005 12:18 AM
"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.
06-23-2005 07:37 AM
Thanks, I like this approach, and actually think I can do it without using GRE tunnels, which will follow the KISS method.
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