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.

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 MSTP VLAN-to-instance mapping condition reported. The relevant technical distinction is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

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 MSTP VLAN-to-instance mapping condition reported. The relevant technical distinction is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

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 MSTP VLAN-to-instance mapping condition reported. The relevant technical distinction is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

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 MSTP VLAN-to-instance mapping. The relevant observable outcome here is: All regional peers report a matching MST region configuration and each VLAN follows its intended instance tree.

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 MSTP VLAN-to-instance mapping. The relevant observable outcome here is: All regional peers report a matching MST region configuration and each VLAN follows its intended instance tree.

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

RSTP maintains alternate port roles that can supply loop-free connectivity after selected path failure. This explains RSTP alternate port failover, but not why the issue in this scenario occurs. The specific mechanism is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

QoS differentiation depends on packet classification, marking trust and congestion-aware queuing. This explains QoS DSCP remarking and trust, but not why the issue in this scenario occurs. The specific mechanism is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

Ordered route-policy matching stops at an applicable node and its permit or deny behavior. This explains Route-policy permit and deny node order, but not why the issue in this scenario occurs. The specific mechanism is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

Misordered nodes can create routing leaks that an apparently correct later deny cannot stop. This consequence is associated more directly with Route-policy permit and deny node order. For the stated conditions the immediate exposure is: Mismatched maps can split a region and defeat planned per-VLAN load balancing.

Deploying dense mode on a sparse WAN may produce unnecessary transient multicast traffic. This consequence is associated more directly with PIM-DM flood and prune behavior. For the stated conditions the immediate exposure is: Mismatched maps can split a region and defeat planned per-VLAN load balancing.

Failing to protect user ports can allow a rogue switch to disrupt campus spanning-tree topology. This consequence is associated more directly with RSTP edge-port BPDU protection. For the stated conditions the immediate exposure is: Mismatched maps can split a region and defeat planned per-VLAN load balancing.

Inspect ACL rule numbers, match counts, attachment direction and permitted/denied test flows. This check would diagnose ACL packet filter rule order and direction, but would not first isolate the described MSTP VLAN-to-instance mapping. Begin with: Compare MST configuration digests, VLAN maps, revisions and CIST boundary state.

Inspect edge-port flags, BPDU-protection events, root changes and MAC-move logs. This check would diagnose RSTP edge-port BPDU protection, but would not first isolate the described MSTP VLAN-to-instance mapping. Begin with: Compare MST configuration digests, VLAN maps, revisions and CIST boundary state.

Inspect port roles, proposal/agreement exchanges, physical link state and failover logs. This check would diagnose RSTP alternate port failover, but would not first isolate the described MSTP VLAN-to-instance mapping. Begin with: Compare MST configuration digests, VLAN maps, revisions and CIST boundary state.

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 MSTP VLAN-to-instance mapping condition reported. The relevant technical distinction is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

Restore valid alternate-port eligibility and verify the supported RSTP rapid convergence procedure. This is a legitimate response to the different issue of RSTP alternate port failover, but it does not correct the specific MSTP VLAN-to-instance mapping condition reported. The relevant technical distinction is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

Correct the unicast or multicast RPF topology so the accepted packet arrives on the expected upstream interface. This is a legitimate response to the different issue of Multicast reverse-path forwarding, but it does not correct the specific MSTP VLAN-to-instance mapping condition reported. The relevant technical distinction is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

Membership entries remain active for subscribed receivers and disappear after intentional leave or expiry. That observation would support a separate case of IGMP last-hop membership queries, not verification of the reported MSTP VLAN-to-instance mapping. The relevant observable outcome here is: All regional peers report a matching MST region configuration and each VLAN follows its intended instance tree.

The intended region shares coherent instance topology and redundant paths remain loop-free. That observation would support a separate case of MSTP region mismatch on trunks, not verification of the reported MSTP VLAN-to-instance mapping. The relevant observable outcome here is: All regional peers report a matching MST region configuration and each VLAN follows its intended instance tree.

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 MSTP VLAN-to-instance mapping. The relevant observable outcome here is: All regional peers report a matching MST region configuration and each VLAN follows its intended instance tree.

A totally stub area suppresses most Type 3 inter-area advertisements while retaining a default summary route. This explains OSPF totally stub area inter-area constraint, but not why the issue in this scenario occurs. The specific mechanism is: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

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: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

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: An MST region's identity includes consistent region parameters and VLAN-to-instance mapping.

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: Mismatched maps can split a region and defeat planned per-VLAN load balancing.

Disabling all BFD checks to suppress authentication errors can undermine route-failure detection. This consequence is associated more directly with BFD authentication mismatch. For the stated conditions the immediate exposure is: Mismatched maps can split a region and defeat planned per-VLAN load balancing.

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: Mismatched maps can split a region and defeat planned per-VLAN load balancing.

Compare (S,G) membership, source route, upstream PIM neighbor and RPF outcome. This check would diagnose Multicast SSM and RPF source path, but would not first isolate the described MSTP VLAN-to-instance mapping. Begin with: Compare MST configuration digests, VLAN maps, revisions and CIST boundary state.

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 MSTP VLAN-to-instance mapping. Begin with: Compare MST configuration digests, VLAN maps, revisions and CIST boundary state.

Inspect route-policy node IDs, if-match criteria, apply clauses and hit counts. This check would diagnose Route-policy permit and deny node order, but would not first isolate the described MSTP VLAN-to-instance mapping. Begin with: Compare MST configuration digests, VLAN maps, revisions and CIST boundary state.