Network & Infrastructure / BGP Policy & Internet Edge
BGP multipath eligibility before ECMP traffic analysis
Two equal-looking BGP advertisements arrive, yet only one next hop is installed. The operator assumes a hardware load-balancing failure before checking whether both paths qualify.
Environment and inputs: BGP speakers and route reflectors; policy syntax, RPKI integration and address-family behavior depend on the implementation. Diagnostic/design example; not tested on production equipment.
Collect the evidence
Compare multipath configuration, path attributes, neighboring AS constraints, next-hop resolution and the installed forwarding group. Record differences that the implementation requires to be equal.
Explain the result
Multiple received paths do not imply multiple forwarding next hops. Multipath selection has additional eligibility rules, and per-flow hashing applies only after a group is actually installed.
Plan the fix
Align the intended paths with documented multipath requirements and hardware limits. Avoid weakening path-consistency checks globally to obtain a larger group for one destination.
Check the result and rollback
Verify the installed group and use several distinct flows to inspect distribution. Revert if paths cross unintended providers, asymmetric stateful boundaries or a failure domain the design excludes.