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):

Note that a MAC-only route can be advertised along with, but independent from, a MAC/IP route for scenarios where the MAC learning over an access network/node is done in the data plane, and independent from ARP snooping that generates a MAC/IP route. In such scenarios, when the ARP entry times out and causes the MAC/IP to be withdrawn, then the MAC information will not be lost.

Thanks a million, Naveen (I also fixed the exercise description)!

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