Hi All,
Sorry for the poor subject, I honestly an not 100% sure how to create a one line summary for this.
Scenario:
Multiple external peers (60+) to which we advertise sets of routes based on BGP communities for well established “sets” (read: We have about 25 routes in total that we selectively advertise). For the purposes of this discussion, let’s assume we have a route 10.0.0.0/24 that we advertise to the outside world.
We utilise two route-reflectors internally. These inject 10.0.0.0/24 as an unreachable route (it gives itself as destination, and has 10.0.0.0/23 unreachable installed since we cannot get functionality on Mikrotik working to install unreachable route) and sets the appropriate community to enable advertising to the outside world. So there are three routes in total:
10.0.0.0/23 - given to all peers.
10.0.0.0/24 - selectively advertised to some peers.
10.0.1.0/24 - selectively advertised to some peers.
We also have a number of downstreams from where we obtain internal routing (and set appropriate communities to NOT advertise these to the outside world).
There are other constraints, and other issues I’d love solve, given the above, but please let’s focus on the immediate problem.
We have a number of downstream routes. Up to now these were always smaller than the encapsulating /24, but one of these routes have now grown to /24. We do not have the ability to from that downstream advertise two /25s (10.0.0.0/25 & 10.0.0.128/25) instead of a single /24 since that originator is outside of our control.
We need to install the advertised from downstream routes into the FIB, and send these to the route reflector (but not peers).
We need to not install the same route from the RR into the FIB, but advertise that route to other peers. Fixing up the route-maps on the RRs to replace it’s own locally injected route with that from the edge router and set the communities is perfectly do-able, and yes, this can probably happen on the edges too, but it then becomes a management nightmare as there are then control functions delegated to edge routers, where it doesn’t belong.