Network failures and convergence for all-active multi-homing

The following figure shows the behavior on the remote PEs (PE3) when there is an ethernet-segment failure.

Figure: All-active multi-homing ES failure

The following steps describe the unicast traffic behavior on PE3:

  1. PE3 can only forward MAC DA = CE2 to both PE1 and PE2 when the MAC advertisement route from PE1 (or PE2) and the set of Ethernet AD per-ES routes and Ethernet AD per-EVI routes from PE1 and PE2 are active at PE3.

  2. In case of a failure between CE2 and PE2, PE2 withdraws its set of Ethernet AD routes and ES route, and PE3 forwards traffic destined for CE2 to PE1 only. PE3 does not need to wait for the withdrawal of the individual MAC.

  3. The same handling is used if the failure was at PE1.

  4. If after step2, PE2 withdraws its MAC advertisement route, PE3 treats traffic to MAC DA = CE2 as unknown unicast, unless PE1 has previously advertised the MAC.

For BUM traffic, the following events trigger a DF election on a PE, and only the DF forwards BUM traffic after the esi-activation-timer expires (if there was a transition from non-DF to DF):

Parent topic: EVPN all-active multi-homing