L2 stretch across the city’s DCI works, but unknown unicast and bro…

Question

L2 stretch across the city’s DCI works, but unknown unicast and broadcast traffic is saturating the WAN links. What troubleshooting focus is appropriate?

Accepted Answer

Detect and mitigate excessive BUM across the L2 DCI—review DF, ingress replication/multicast design, and whether L2 stretch is still required — L2 stretch turns the WAN into another flood domain for BUM if you are not careful—like leaving every firehose pointed at the metro pipe. Hunt DF behavior, replication design, and whether that segment truly needs L2 across sites. Sometimes Type-5 L3 DCI is the calmer fix.

Answer

Disable all EVPN Type-5 routes because they are the sole source of BUM on L2 stretch

Answer

Increase spanning-tree max-age citywide as the only supported BUM control for VXLAN DCI

Answer

Shutdown every VTEP loopback so BUM cannot encapsulate toward the remote site

L2 stretch across the city’s DCI works, but unknown unicast and broadcast traffic is saturating the WAN links. What troubleshooting focus is appropriate?

Short Explanation

Full Explanation