On Generating EVPN MAC/IP Routes
Naveen Kumar Devaraj was reading my Integrated Routing and Bridging (IRB) with EVPN MAC-VRF Instances lab exercise and spotted this detail:
Arista EOS originates MAC-IP routes with and without IP addresses, effectively doubling the size of the EVPN BGP table
He kindly wrote a LinkedIn comment explaining that behavior:
This is by design since the triggers for these two types of routes are fundamentally different. A MAC table update triggers and aligns with a MAC-Only route, while an ARP table update triggers and aligns with a MAC+IP route. They are kept separate in EVPN for the exact same reason ARP and MAC tables are separate, as we know traditionally.
You know I had to check that against the RFC 7432, right? Here’s what it says in Section 9.2.1 (ARP and ND):
Thanks a million, Naveen (I also fixed the exercise description)!
Thanks for getting down to this level of detail Ivan, it's interesting to evaluate the tradeoff between table size &
Back in the bad old days of RSTP & IRB, it was critical to ensure that ARP aging timers & MAC aging timers were set to the same value on router-flavored switches in order to avoid unknown unicast flooding.
EVPN handles BUM traffic a lot better, but I'd imagine it's still good practice to align these two timers to avoid similar issues. & you can add IPv6 neighbor discovery stale timers to the list too...
Also worth noting that this technique might double the number of EVPN RIB & FIB entries, but MAC entries generally don't consume as many hardware resources as full type 5 routes so the overhead to add the additional MAC routes is lower than it may appear at first glance.