BGP-EVPN MAC-mobility

EVPN defines a mechanism to allow the smooth mobility of MAC addresses from an NVE to another NVE. The 7750 SR, 7450 ESS, and 7950 XRS support this procedure as well as the MAC-mobility extended community in MAC advertisement routes as follows:

The router honors and generates the SEQ (Sequence) number in the MAC mobility extended community for MAC moves.
When a MAC is EVPN-learned and it is attempted to be learned locally, a BGP update is sent with SEQ number changed to ‟previous SEQ”+1 (exception: MAC duplication num-moves value is reached).
SEQ number = zero or no MAC mobility ext-community are interpreted as sequence zero.
In case of mobility, the following MAC selection procedure is followed:
- If a PE has two or more active remote EVPN routes for the same MAC (VNI can be the same or different), the highest SEQ number is selected. The tie-breaker is the lowest IP (BGP NH IP).
- If a PE has two or more active EVPN routes and it is the originator of one of them, the highest SEQ number is selected. The tie-breaker is the lowest IP (BGP NH IP of the remote route is compared to the local system address).

Note: When EVPN multihoming is used in EVPN-MPLS, the ESI is compared to determine whether a MAC received from two different PEs has to be processed within the context of MAC mobility or multihoming. Two MAC routes that are associated with the same remote or local ESI but different PEs are considered reachable through all those PEs. Mobility procedures are not triggered as long as the MAC route still belongs to the same ESI.