The challenge
The network had several upstream and peering relationships, but path selection had evolved through individual changes rather than one documented policy.
The review
Routes, communities, local preference, filters, direct peers, route servers and failure behaviour were examined together. Hidden dependencies and inconsistent IPv4 and IPv6 treatment were identified.
The design
A policy hierarchy defined preferred direct peers, exchange routes, primary transit and backup transit. Prefix controls, RPKI, maximum-prefix behaviour and monitoring requirements were documented.
The result
Engineers could explain why a path was selected, predict failover and validate changes against a common design rather than relying on inherited configuration.