How do I link two telco provided MPLS networks? EIGRP?

Answered Question
May 27th, 2010

Hello,

Often browse these forums, but first time posting...

I have two telco provided MPLS networks which I need to link together. I'm assuming that the telcos will be using BGP on their MPLS and I have got 3750 switches at the site where the two MPLS networks both have presence. So I'm thinking I could use EIGRP on the 3750's to redistribute the two BGP AS into EIGRP and therfore share the routing tables between them... ?

We have two sites where the MPLS netowrks meet so I'd like to use one as primary route and one as secondary.

I've attahed a diagram which will probably make more sense than my waffle above! Was hoping some one could advise if I'm on the right track and if any one has any sample configs etc for the EIGRP on the 3750's ?

Cheers,

Mike

I have this problem too.
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Correct Answer by milan.kulik about 6 years 6 months ago

Hi,

IMHO, the most flexible way would be running BGP between your L3 switches and both provider routers in  New York and Baton Rouge (using two different private AS numbers).

This way you'd get an absolute control what would be advertised between the two provider clouds.

And could use as-prepending to decide, which path would be preferred, e.g.

And filter out any prefix, if necessary.

It might be a little complicated to discuss in the beginning with the providers (to agree on the AS numbers you'd use, etc.) but if both of them behave correctly (i.e., using public AS numbers in their backbone only, and any private AS number agreed with you), this would work without problems.

BR,

Milan

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Giuseppe Larosa Fri, 05/28/2010 - 04:31

Hello Mike,

given the topology you have provided the two MPLS clouds are not overlapping but they are serving different sites.

if the two providers are using private AS numbers (in range 64512-65535) and you have one single AS number assigned to your devices you can think of using an iBGP session between the two C3750 in the two multihomed sites.

Redistribution in EIGRP may be useful for routing from main sites internal devices but it is not needed for BGP routes propagation.

But a default route could do the job without needing redistribution of BGP routes into local IGP.

Another possible approach to avoid to mix routes of sites served by ISPA and sites served by ISPB could be to advertise a default route or appopriate summary routes to represent all the prefixes of cloud A to cloud B and viceversa.

This would allow to handle possible AS path filters used by providers that could block simple propagation of eBGP routes from one cloud to the other.

In any case you could use AS path prepending to make main site B routes less preferred then main site A routes.

You should prepend your own AS number some times.

The service provider may change each AS number instance with own AS number (typically done with neigh ... as-override on SP side)

Hope to help

Giuseppe

mtjones83 Fri, 05/28/2010 - 06:48

Thank you for your reply, Guiseppe.

The two MPLS netowrks are fully managed by the telcos, so I do not have direct access to their routers. I was looking for a simple way to link the two networks with minimum contact with the ISP's if possible. In reality this will be a temporary solution for at most 12 months when we will then replace one of the MPLS netowrks with links into the others cloud and have a single global MPLS.

Currently the UK network can see all devices in New York & Baton Rouge, but the remote sites on both sides of the atlantic can not see each other.

The EIGRP 100 in the UK is already configured and working.

I can ping both networks from the C3750 in Baton Rouge but when I try and use this switch as a default gateway between the networks it doesn't work?

gatlin007 Fri, 05/28/2010 - 07:50

Reaching out to the telcos and getting your remote site prefixes properly routed would be the best solution; however I understand how painful that can be.

If your switches support GRE you could install tunnels between your sites, taking the routing decision for remote sites out of the MPLS VPN clouds. 

Christopher Gatlin

http://travelingtech.net

Correct Answer
milan.kulik Sat, 05/29/2010 - 23:29

Hi,

IMHO, the most flexible way would be running BGP between your L3 switches and both provider routers in  New York and Baton Rouge (using two different private AS numbers).

This way you'd get an absolute control what would be advertised between the two provider clouds.

And could use as-prepending to decide, which path would be preferred, e.g.

And filter out any prefix, if necessary.

It might be a little complicated to discuss in the beginning with the providers (to agree on the AS numbers you'd use, etc.) but if both of them behave correctly (i.e., using public AS numbers in their backbone only, and any private AS number agreed with you), this would work without problems.

BR,

Milan

mtjones83 Tue, 06/01/2010 - 11:41

I think I'm gonna go for EIGRP...

We already use EIGRP to learn the BT MPLS routes on the core switch in Warrington, so it makes sense to go the same way. I've found a good guy at BT who will help with the changes they need to make and he's happy to use EIGRP... just need to find a simlar helpful engineer at AT&T !!!

Thanks for all you help.

Mike

shaileshgovekar Tue, 01/24/2012 - 06:46

Hi Mike,

Just wondering if you got this setup working between AT&T and BT MPLS

Regards

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