Using Designated Forwarder (DF) election in EVPN all-active multi-homing prevents duplicate packets on the multi-homed CE. The DF election procedure elects one DF PE per ESI per service; the rest of the PEs are non-DF for the ESI and service. Only the DF forwards BUM traffic from the EVPN network toward the ES SAPs (the multi-homed CE). The non-DF PEs do not forward BUM traffic to the local ES SAPs.
The following figure shows the need for DF election in all-active multi-homing.
Figure: DF election
Note:
BUM traffic from the CE to the network and known unicast traffic in any direction is allowed on both the DF and non-DF PEs.