Hello there,
s702 wrote:
I want to make sure that AS100 advertises BOTH default routes to AS65124.
Are there two or one Option A interconnects between AS100 and AS65124?
One interconnect == 1 logical interface inside 1 distinct VRF. Two logical interfaces inside one VRF does not count as two interconnects.
With two Option A logical interconnects, AS65124 can easily have two 0/0 announced from AS100.
With single logical interconnect, it becomes non-trivial. What "next-hop" value to You expect to be for each of these 0/0 routes as seen in BGP Update going from AS100 to AS65124?
By default, AS100 will set "next-hop" value to own egress interface' IP address for both 0/0 routes, so it does not make a difference if AS100 sends You one or two 0/0s as they would be both the same from forwarding perspective.
But technically, You could have two distinct 0/0 routes coming to AS65124 from AS100 if You do:
1/ add "accept-remote-nexthop" to AS65124 ASBRs
2/ negotiate with AS100 so that they set "next-hop" for each of 0/0 to something different than own egress interface IP
3/ negotiate with AS100 that they ALSO send You BGP /32 routes for remote "next-hops" of 0/0 routes.
However, from AS65124->AS100 forwarding perspective it won't be much different. It would be slightly different from failover perspective since You would have two copies of 0/0 route so if AS100 withdraws one, AS65124 does not have to wait for AS100 to reannounce another 0/0. You could achieve the same with static 0/0 preference 171.
Internally, if AS100 uses unique RD per PE (best practice) it would have two 0/0 routes in VRF facing AS65124, and would load-balance or not depending on their config (routing-instances BLAH routing-options multipath vpn-unequal-cost].
HTH
Thx
Alex