Network & Infrastructure / EVPN, VXLAN & Data Center Fabrics
EVPN split horizon and duplicate BUM reflection
A multihomed segment sees repeated broadcast frames after a new external bridge is connected. Traffic may return to the same segment through an unintended overlay or local bridge path.
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
Trace one frame's ingress attachment, replication destinations and egress segment identity. Check split-horizon state and external Layer-2 connectivity without generating a broad broadcast load.
Explain the result
Split-horizon mechanisms prevent specific forms of reflection in the designed multihoming topology. An extra unmodeled bridge can bypass those assumptions or create a separate loop.
Plan the fix
Remove the unintended connection and correct segment mapping according to the supported split-horizon model. Avoid disabling loop protection to recover a single path.
Check the result and rollback
Confirm one expected delivery per receiver under normal operation and controlled failover. Restore prior attachment state if containment removes the legitimate service, and preserve packet evidence of the loop origin.