What is a design consideration of policy-based routing?

PBR is a unidirectional, inbound policy applied on a single interface and does not require symmetric or matching configuration at the remote end of a GRE tunnel.

While PBR adds per-packet processing overhead on the router, its fundamental design concern is forwarding consistency during reconvergence, not network-wide scalability.

PBR overrides destination-based routing on a per-router, per-interface basis without propagating its forwarding logic to neighboring routers; during a topology change and reconvergence, one router may still apply a PBR policy pointing traffic toward a next-hop that other routers are simultaneously rerouting away from, creating a transient microloop. This asymmetric forwarding behavior is a well-documented design risk of PBR deployments.

PBR has no mechanism for failure detection; faster failure detection is achieved through tools such as BFD or tuning IGP hello and dead timers.