The 7210 SAS SR OS supports only single-active multi-homing on access LAG SAPs and regular SAPs for a specified VPLS service. For LAG SAPs, the CE is configured with a different LAG to each PE in the ES (in contrast to a single LAG in an all-active multi-homing).
The following SR OS procedures support EVPN single-active multi-homing for a specified ES:
DF election
The DF election in single-active multi-homing determines the forwarding for BUM traffic from the EVPN network to the ES CE. DF election also determines the forwarding of any traffic (unicast or BUM) in any direction (to or from the CE).
backup PE
In single-active multi-homing, the remote PEs do not perform aliasing to the PEs in the ES. The remote PEs identify the DF based on the MAC routes and send the unicast flows for the ES to the PE in the DF. The remote PEs also program a backup PE as an alternative next-hop for the remote ESI in case of failure. This is in accordance with the Backup PE procedure, defined in RFC 7432.
The following figure shows an example backup PE for PE3.
Figure: Backup PE