EIGRP over MPLS

Answered Question
Jul 21st, 2009
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Hello, I have 3 offices that are connected to a MPLS network. Each office link to the cloud is a different subnet. So my question is now how can I configure EIGRP if each router is on a separate subnet? The neighrbors will not be established by default since the links are on different subnets right? Any help is greatly appreciated. Thanks

Correct Answer by Edison Ortiz about 8 years 3 days ago

Hi Bart,


You need to have a common subnet in your MPLS facing interface as you are peering with the MPLS provider, not your remote sites.


If you want to advertise your EIGRP routes from each remote, you will need to redistribute these routes into the CE<->PE routing protocol that is being used and viceversa.


HTH,


__


Edison

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Correct Answer
Edison Ortiz Tue, 07/21/2009 - 10:56
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Hi Bart,


You need to have a common subnet in your MPLS facing interface as you are peering with the MPLS provider, not your remote sites.


If you want to advertise your EIGRP routes from each remote, you will need to redistribute these routes into the CE<->PE routing protocol that is being used and viceversa.


HTH,


__


Edison

bsudol79p Tue, 07/21/2009 - 11:09
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That is what I was afraid of. The interfaces that are connected to the MPLS are not on common subnet. Each interface to the cloud has a /30 so they are Point to Point. So there is no way of running EIGPR unless the ISP puts the links on common subnet? Thanks again


EXAMPLE Links to the cloud:

Chicago 10.10.10.2 /30

Minnesota 10.10.10.4 /30

NY 10.10.10.6 /30

Edison Ortiz Wed, 07/22/2009 - 04:44
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Hi Bart,


That's your typical L3 MPLS-VPN design. You are directly connected to your provider router in a point-to-point connection hence both routers need to be a common subnet. You aren't in a common subnet with your remote routers as they are connected with their respective provider router on the same point-to-point connection design.


If you want to have your remote routers connected directly to each other in order to run EIGRP, then you have to configure GRE tunnels for the EIGRP adjacency.


There is also L2 MPLS-VPN service available where the ISP is transparent to the customer and you will be able to see your remote routers as directly connected.


HTH,


__


Edison.




neilobrien Tue, 07/21/2009 - 12:57
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redistribution into the providers routing protocol would certainly be the best way to get your routes across however you could run a GRE tunnel between the 3 routers and run your own routing protocol through the tunnel.


I've never tried this so i can't vouch for it's reliability.

vmiller Wed, 07/22/2009 - 06:46
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As long as MPLS is working, you don't have an issue. You do need to have the MPLS Layer 3 definition at the remotes learn the local subnets either via either network statements or redistribution. That BGP instance at the remote will insure that your local are available. You may not see them since providers usually just send a default. The PE routers do all the work.

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