Network & Infrastructure / BGP Policy & Internet Edge
Allow-own-AS exceptions and loop prevention at a migration edge
During a provider migration, a site rejects routes containing its own ASN. Allowing its ASN indiscriminately might restore reachability while weakening a useful loop-prevention boundary.
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
Capture the complete AS path, migration topology, intended reentry points and exact rejected prefixes. Establish why the local ASN appears and whether the behavior is temporary.
Explain the result
AS-path loop checks prevent a router from accepting an advertisement that may already have traversed its domain. An exception must be justified by topology, not merely by a missing route.
Plan the fix
Prefer a documented migration design with narrowly scoped acceptance, prefix filtering and a retirement date. Review any provider AS-override alternative and its interaction with site identifiers.
Check the result and rollback
Test a legitimate migration route and a deliberately looping advertisement in isolation. Remove the exception when migration ends; revert immediately if unexpected site routes become acceptable.