Routing Problems - Routing Loops - MPLS, BGP & EIGRP

Unanswered Question
May 2nd, 2010

I've got an MPLS network that is experiencing routing loops every 3-4 hours.  Our Service Provider says they are seeing advertisements from our routers for routes that are not in that part of the network.  When we check our routers, they say the opposite.  Is it possible for a router to advertise a route that is not in its network back to the router it got the advertisement from even with split-horizon enabled?  We are running eigrp on our local networks and the Service Provider is redistributing into bgp.

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Giuseppe Larosa Sun, 05/02/2010 - 10:55

Hello Blamb,


how are the VPN sites interconnected?

there is any "direct" link between sites that joins the EIGRP domains of the different sites?


Also, is any VPN site multihomed, that is there are two CE routers connecting in EIGRP to SP networks

This can be the origin of the issue.


You should look at EIGRP topology database for prefixes that can appear at the same time as EIGRP  routes coming from SP network and as EIGRP internal routes if any direct link between sites exist.


SP can use site of origin SOO BGP extended attribute as a way to deal with VPN redundancy at sites, to avoid unwanted re-injection of routes in multi CE ,per VPN site, topologies.


The SP can configure its routers so that it can rebuild EIGRP routes for remote sites IP subnets in order to avoid to have them appear as external routes.


How do you see the remote site routes coming from SP network?

Are they internal or external routes?


Every 3-4 hours a loop event happen this is an info that can be useful but at the moment it does not provide any insight.


Have you tried to implement distribute-list in EIGRP to advertise out interfaces of CE routers towards SP PE nodes only the IP prefixes local to the site?

This could help in solving the issue.


Hope to help

Giuseppe

blamb Sun, 05/02/2010 - 14:21

No direct links between VPN sites. Most of our VPN connections are a single E1 or T1. There is one site that has two sites splitting off from the SP's router. All three routers are apparently on the same subnet. We are checking out SIA stuck-in-active issues that occur there but the SIA issues are present even when the problem isn't.


I'll have to talk to SP about SOO BGP extended attribute.


The routes from SP appear as internal.


I'm looking at creating a distribute-list now. Was never necessary before.


Thanks for help

blamb

bgandhi Sun, 05/02/2010 - 21:04

Is it possible for you to share the config. Also, just a recomemndation to consider, you may try converting your site as stub conencted. This would prevent by default learnt routes to any other peers. However, please plan it properly else you may face outage.


Regards,

Bhavesh

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