Network & Infrastructure / EVPN, VXLAN & Data Center Fabrics
VXLAN encapsulation MTU and selective tenant packet loss
Small overlay packets succeed while larger application responses fail between racks. The underlay may not accommodate the tenant packet plus outer encapsulation and link-specific overhead.
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
Record tenant MTU, tunnel encapsulation format, underlay interface MTUs and ICMP feedback. Test relevant sizes across each ECMP path rather than assuming one successful probe represents the fabric.
Explain the result
Encapsulation increases the packet carried by the underlay. A mismatch can cause drops or fragmentation depending on stack behavior, and blocked feedback can make the failure look like an application timeout.
Plan the fix
Define a consistent end-to-end size budget and correct the constrained segment or tenant policy. Include additional tags and outer IPv6 when those are actually present.
Check the result and rollback
Validate full-size packets on every supported path and after failover. Restore previous settings if increasing MTU introduces incompatibility or a smaller alternate link remains outside the tested budget.