Compare received candidate paths, LOCAL_PREF values, route policy and installed best path. This check would diagnose BGP local preference internal egress, but would not first isolate the described RSTP edge-port BPDU protection. Begin with: Inspect edge-port flags, BPDU-protection events, root changes and MAC-move logs.

Inspect root bridge ID, path cost, port roles and current bridge priorities. This check would diagnose RSTP root bridge location, but would not first isolate the described RSTP edge-port BPDU protection. Begin with: Inspect edge-port flags, BPDU-protection events, root changes and MAC-move logs.

Inspect stack role, heartbeat, split-brain detection state and inter-member link health. This check would diagnose Switch stacking split-brain, but would not first isolate the described RSTP edge-port BPDU protection. Begin with: Inspect edge-port flags, BPDU-protection events, root changes and MAC-move logs.

Run a capacity-focused RF design with appropriate channel reuse, transmit power and channel width. This is a legitimate response to the different issue of High-density WLAN RF plan, but it does not correct the specific RSTP alternate port failover condition reported. The relevant technical distinction is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Set reviewed RSTP bridge priorities so an appropriate resilient core device remains root. This is a legitimate response to the different issue of RSTP root bridge location, but it does not correct the specific RSTP alternate port failover condition reported. The relevant technical distinction is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Align supported RP discovery or static RP assignments for matching multicast groups across the domain. This is a legitimate response to the different issue of PIM-SM rendezvous-point mismatch, but it does not correct the specific RSTP alternate port failover condition reported. The relevant technical distinction is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

An unauthorized bridge is blocked or the port enters its defined protected state without changing the core root. That observation would support a separate case of RSTP edge-port BPDU protection, not verification of the reported RSTP alternate port failover. The relevant observable outcome here is: An authorized failover moves the alternate link to forwarding without creating a loop.

Tenant routes remain isolated and permitted cross-instance services follow explicit controlled paths. That observation would support a separate case of VRF route isolation, not verification of the reported RSTP alternate port failover. The relevant observable outcome here is: An authorized failover moves the alternate link to forwarding without creating a loop.

Tagged management prefixes follow the intended permit/deny outcome without affecting unrelated production routes. That observation would support a separate case of BGP community filtering in routing control, not verification of the reported RSTP alternate port failover. The relevant observable outcome here is: An authorized failover moves the alternate link to forwarding without creating a loop.

Uncontrolled mutual route import can form routing feedback loops and unstable route selection. This explains Route import feedback loop, but not why the issue in this scenario occurs. The specific mechanism is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

MSTP recognizes region boundaries through region name, revision and VLAN mapping digest. This explains MSTP region mismatch on trunks, but not why the issue in this scenario occurs. The specific mechanism is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Stacking combines multiple devices into a logical control plane and requires protection against split brain. This explains Switch stacking split-brain, but not why the issue in this scenario occurs. The specific mechanism is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Uncontrolled reimport can create persistent false reachability after a primary path fails. This consequence is associated more directly with Redistribution route tag loop avoidance. For the stated conditions the immediate exposure is: Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve.

Mismatched maps can split a region and defeat planned per-VLAN load balancing. This consequence is associated more directly with MSTP VLAN-to-instance mapping. For the stated conditions the immediate exposure is: Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve.

An accidental boundary can change port roles and send traffic over unintended links. This consequence is associated more directly with MSTP region mismatch on trunks. For the stated conditions the immediate exposure is: Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve.

Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover. This check would diagnose CSS chassis clustering and failover, but would not first isolate the described RSTP alternate port failover. Begin with: Inspect port roles, proposal/agreement exchanges, physical link state and failover logs.

Inspect stack role, heartbeat, split-brain detection state and inter-member link health. This check would diagnose Switch stacking split-brain, but would not first isolate the described RSTP alternate port failover. Begin with: Inspect port roles, proposal/agreement exchanges, physical link state and failover logs.

Inspect vpn-instance bindings, per-instance routing tables and cross-instance route-policy. This check would diagnose VRF route isolation, but would not first isolate the described RSTP alternate port failover. Begin with: Inspect port roles, proposal/agreement exchanges, physical link state and failover logs.

Implement supported stack split-brain detection and redundant stack interconnects before production. This is a legitimate response to the different issue of Switch stacking split-brain, but it does not correct the specific RSTP alternate port failover condition reported. The relevant technical distinction is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Build a supported source-rooted multicast path using IGMPv3 source membership and PIM RPF toward S. This is a legitimate response to the different issue of Multicast SSM and RPF source path, but it does not correct the specific RSTP alternate port failover condition reported. The relevant technical distinction is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Validate supported CSS inter-chassis links, roles, redundancy and a controlled master-failover test. This is a legitimate response to the different issue of CSS chassis clustering and failover, but it does not correct the specific RSTP alternate port failover condition reported. The relevant technical distinction is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

A stack-link fault produces the designed protective isolation with one coherent active forwarding system. That observation would support a separate case of Switch stacking split-brain, not verification of the reported RSTP alternate port failover. The relevant observable outcome here is: An authorized failover moves the alternate link to forwarding without creating a loop.

All regional peers report a matching MST region configuration and each VLAN follows its intended instance tree. That observation would support a separate case of MSTP VLAN-to-instance mapping, not verification of the reported RSTP alternate port failover. The relevant observable outcome here is: An authorized failover moves the alternate link to forwarding without creating a loop.

Approved operators log in with accountable roles while unauthorized commands and Telnet access fail. That observation would support a separate case of Device management AAA and SSH security, not verification of the reported RSTP alternate port failover. The relevant observable outcome here is: An authorized failover moves the alternate link to forwarding without creating a loop.

An SD-WAN overlay can select among heterogeneous underlay links using measured application path quality. This explains SD-WAN underlay and application steering, but not why the issue in this scenario occurs. The specific mechanism is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

Edge-port safeguards prevent unintended bridge participation where endpoint-only connections are expected. This explains RSTP edge-port BPDU protection, but not why the issue in this scenario occurs. The specific mechanism is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

MSTP recognizes region boundaries through region name, revision and VLAN mapping digest. This explains MSTP region mismatch on trunks, but not why the issue in this scenario occurs. The specific mechanism is: RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure.

An accidental boundary can change port roles and send traffic over unintended links. This consequence is associated more directly with MSTP region mismatch on trunks. For the stated conditions the immediate exposure is: Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve.

Untested clustering can leave a single point of failure despite two physical chassis. This consequence is associated more directly with CSS chassis clustering and failover. For the stated conditions the immediate exposure is: Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve.

Any-source joins cannot always represent source-specific subscriptions and may allow unwanted streams. This consequence is associated more directly with IGMPv3 source-specific membership. For the stated conditions the immediate exposure is: Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve.

Inspect AP address, controller discovery, CAPWAP control status and AC join logs. This check would diagnose WLAN AC and Fit AP CAPWAP, but would not first isolate the described RSTP alternate port failover. Begin with: Inspect port roles, proposal/agreement exchanges, physical link state and failover logs.

Inspect region digest, MSTI states, instance root priorities and boundary-port indicators. This check would diagnose MSTP region mismatch on trunks, but would not first isolate the described RSTP alternate port failover. Begin with: Inspect port roles, proposal/agreement exchanges, physical link state and failover logs.

Inspect PBR classifier, interface direction, policy hits and a traffic trace. This check would diagnose Policy-based routing for approved application, but would not first isolate the described RSTP alternate port failover. Begin with: Inspect port roles, proposal/agreement exchanges, physical link state and failover logs.