EVPN Multi-Active Multihoming#

Jeffrey Zhang, Changwang Lin, Jorge Rabadan (individual draft, BESS)

• Why: EVPN offers All-Active or Single-Active multihoming today; operators want a hybrid — a subset of PEs active and load-balanced, the rest standing by for fast failover, without full active-active fanout.
• What: Multi-Active mode for a multihomed Ethernet Segment: PEs with higher configured preference operate All-Active (ingress PEs load-balance to them); non-preferred PEs stay Single-Active/inactive and take over on failure of the preferred set.
• How: Preference is signaled in the DF Election Extended Community (in ES routes); preferred PEs signal P=1/B=0 in the L2-Attribute Extended Community (in Ethernet A-D per-EVI routes) so ingress PEs load-balance to them, while non-preferred PEs signal P=0 and are excluded from DF candidacy via the AC-Influenced DF Election Capability. All PEs (including non-preferred) keep signaling All-Active in the ESI label Extended Community for backward compatibility. Strict-mode (only equal-top-preference PEs active) and loose-mode (M preferred PEs, possibly different values) variants are defined. Only the MHES's own PEs need to understand the mode; other PEs act on the P/B bits as usual.
• Where applicable: EVPN multihoming deployments in DC access and DCI. Early individual draft (-00) seeking comments; authors believe there is no backward-compatibility issue and are asking the WG to scrutinize that claim.