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tmcgovern_cccis
Beginner

Re-Routing traffic on MPLS CE when there are no BGP neighbor issues

At each of our sites we have dual MPLS providers, each connected to their own dedicated CE routers. We are running eBGP with each provider's PE, and iBGP between our two CE routers. All works well under normal circumstances. If a single provider's circuit goes down and the BGP neighbor is lost, traffic is automatically re-routed via the other CE and provider. However, often times we encounter a situation whereby issues deep within the provider MPLS cloud (such as routing issues or failed links) do not materalize on our CE routers - no circuit outages or BGP neighbor loss. Thus traffic continues to be routed via the troubled provider and is black holed deep within their network. The only solution for this is to manually shutdown the eBGP neighbor on the CE connected to the troubled provider so that traffic takes the alternate path learned via iBGP to the other provider.

Are there any mechanisms we could configure on our CE routers to monitor remote sites to make sure that the forwarding path is indeed intact despite what the PE eBGP peer tells us ? If a forwarding path is then determined to be invalid, could a configuration change be initiated to shutdown the peer so traffic would be re-routed through the other provider ?

4 REPLIES 4
SlevinKelevra
Beginner

No, not as far as i know, your still getting both routes from both ISP's, BGP does not know if one ISP has problems. Would be cool though, if you could determine through somekind of IP SLA setup that one site has deep packetloss and changes the weight dynamicly and that the router prepends your AS times 10. Would be 2 much to ask i think ^^

There should be a way to do this using IP SLA and EEM scripts.

Thanks.

Simon Brooks
Beginner

Use ip sla to monitor remote site. Track this as an object and attach to a host route using the pe ip as the host ip;

Ip route x.x.x.x 255.255.255.255 x.x.x.x track 1

Have a pre-fix attached to a route map for that host route;

Ip prefix-list BGPFAIL x.x.x.x/32

Add route map-
Route-map BGPFAIL
match ip prefix list BGPFAIL

Add a command to the ebgp neighbour;

Neighbour x.x.x.x fall-over route-map BGPFAIL

Sent from Cisco Technical Support Android App

Simon Brooks
Beginner

Forgot to add.

Have a static route for remote site ip defined in sla so it doesnt default route to ibgp neighbour. Also dont advertise that route to ibgp neighbour.!

Sent from Cisco Technical Support Android App