Network & Infrastructure / EVPN, VXLAN & Data Center Fabrics
Symmetric IRB: diagnose a missing L3 VNI on one leaf
Same-subnet communication succeeds across the overlay, while inter-subnet traffic fails only through one destination leaf. Its L2 VNIs may be correct but the routed tenant context incomplete.
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 source bridge, tenant VRF, L3 VNI, remote router MAC and destination bridge mappings. Compare route installation and encapsulation with a functioning leaf in the same tenant.
Explain the result
Symmetric IRB uses a routed overlay context between VTEPs in addition to local bridge domains. Missing L3 context can leave working Layer-2 transport and broken routed reachability simultaneously.
Plan the fix
Align the VRF-to-L3-VNI association and required route import/export policy using the implementation's supported IRB model. Avoid mixing symmetric and asymmetric assumptions in an undocumented template.
Check the result and rollback
Test inter-subnet traffic in both directions and after a workload move. Revert if the corrected mapping imports another tenant's routes or creates unresolved remote router next hops.