Routing

Hi all,

Thanks for taking the time to read my question.

I am building an MPLS-EVPN environment with 4 devices (2x MX 2x EX) and they will be connected full mesh logically. 

However, there is a layer1 DWDM network below it. This makes me able to connect them full mesh using only 3 fiber pairs.

See attached image 1.

The problem i am running into is that exported routes will only be imported by the neighboring router but are not forwarded (exported again, route reflection) to the next router.

This causes no problem as long as all links are up as all routers are connected to each router. But if one of the fibre connections breaks, one router will have to export its imported routes from the other router (route reflection)

I think this might not be possible. Any imported route will get a "secondary route" tag and these routes cannot be exported again. 

Is there a creative way to work around this? My DWDM system is full (only 2 free channels) so i am very limited in layer1 adjustments.

Hi, 

I believe there would be 2 standard methods:

1. Full mesh iBGP

2. Resilient Route Reflectors

You would need an IGP running to provide reachabiity of loopback addresses on which BGP would be peering.

Failure of one fibre would still provide IGP reachability and thus BGP neighbor after re-convergence.

Cheers,

Ashvin

Full mesh iBGP ofcourse... Why didnt i think of that 🙂

Thanks! Works great.