Network & Infrastructure / EVPN, VXLAN & Data Center Fabrics
Designated-forwarder election and BUM loss on a multihomed segment
Remote broadcast traffic disappears during a multihoming event even though known unicast recovers. Designated-forwarder state can be inconsistent or converge differently from ordinary MAC reachability.
Environment and inputs: BGP EVPN overlays on a routed underlay; supported route types and multihoming behavior depend on the network OS. Diagnostic/design example; not tested on production equipment.
Collect the evidence
Capture Ethernet segment membership, DF election result, VLAN or service carving and BUM forwarding counters on both leaves. Record exact failure and restoration timestamps.
Explain the result
DF selection controls delivery of certain multi-destination traffic toward a shared segment. A functioning unicast path does not prove the correct leaf is delivering the affected BUM traffic.
Plan the fix
Align supported DF election options and segment membership, then review the intended convergence behavior. Do not force both leaves to forward every BUM packet as a workaround.
Check the result and rollback
Validate ARP discovery and broadcast-sensitive applications during each link and leaf failure. Revert if duplicate delivery rises or DF ownership becomes unstable after restoration.