Network & Infrastructure / EVPN, VXLAN & Data Center Fabrics
Asymmetric IRB and the cost of remote subnet presence
A leaf can route to one remote subnet but not another after tenant growth. The chosen asymmetric design may require local bridge context for remote destination subnets that was never provisioned.
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
Inventory tenant subnets, instantiated bridge domains, per-leaf VNI mappings and hardware table consumption. Compare actual deployment with the selected IRB forwarding model.
Explain the result
Asymmetric and symmetric IRB place different requirements on remote subnet presence and routed transport. A missing bridge domain can be a design dependency rather than a random BGP import failure.
Plan the fix
Either provision the required context within supported scale or plan a reviewed migration to an appropriate routed overlay model. Do not add every possible subnet without capacity analysis.
Check the result and rollback
Validate all intended subnet pairs and measure MAC, neighbor and route table growth. Restore the previous rollout if resource headroom falls below the agreed failure and growth reserve.