Inspect group-to-RP mapping, PIM neighbor state and (*,G) incoming interface. This check would diagnose PIM-SM rendezvous-point mismatch, but would not first isolate the described Switch stacking split-brain. Begin with: Inspect stack role, heartbeat, split-brain detection state and inter-member link health.

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 Switch stacking split-brain. Begin with: Inspect stack role, heartbeat, split-brain detection state and inter-member link health.

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 Switch stacking split-brain. Begin with: Inspect stack role, heartbeat, split-brain detection state and inter-member link health.

Tune approved OSPF link costs to represent the intended path preference and re-evaluate SPF. This is a legitimate response to the different issue of OSPF SPF path-cost comparison, but it does not correct the specific CSS chassis clustering and failover condition reported. The relevant technical distinction is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

Apply appropriate RSTP edge-port and BPDU protection policies while preserving legitimate uplink roles. This is a legitimate response to the different issue of RSTP edge-port BPDU protection, but it does not correct the specific CSS chassis clustering and failover condition reported. The relevant technical distinction is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

Set the Huawei ip ip-prefix network and greater-equal/less-equal bounds to the precise permitted prefixes. This is a legitimate response to the different issue of Prefix-list network and mask matching, but it does not correct the specific CSS chassis clustering and failover condition reported. The relevant technical distinction is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

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 CSS chassis clustering and failover. The relevant observable outcome here is: A member failover preserves approved forwarding and the CSS reports healthy single-system state.

The RP learns the new source and downstream receivers obtain traffic after registration. That observation would support a separate case of PIM first-hop source registration, not verification of the reported CSS chassis clustering and failover. The relevant observable outcome here is: A member failover preserves approved forwarding and the CSS reports healthy single-system state.

Root-port selection and link topology match the designed forwarding tree without a Layer 2 loop. That observation would support a separate case of RSTP root bridge location, not verification of the reported CSS chassis clustering and failover. The relevant observable outcome here is: A member failover preserves approved forwarding and the CSS reports healthy single-system state.

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: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

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: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

PIM-SM any-source multicast uses a rendezvous point to connect new sources and receivers. This explains PIM-SM rendezvous-point mismatch, but not why the issue in this scenario occurs. The specific mechanism is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

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

A Full adjacency is not proof that external prefixes have been injected into OSPF. This consequence is associated more directly with OSPF type-5 external advertisement. For the stated conditions the immediate exposure is: Untested clustering can leave a single point of failure despite two physical chassis.

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: Untested clustering can leave a single point of failure despite two physical chassis.

Inspect (*,G) and (S,G) state, SPT flags, source RPF and join/prune counters. This check would diagnose PIM-SM RPT to SPT switchover, but would not first isolate the described CSS chassis clustering and failover. Begin with: Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover.

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 CSS chassis clustering and failover. Begin with: Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover.

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 CSS chassis clustering and failover. Begin with: Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover.

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 CSS chassis clustering and failover condition reported. The relevant technical distinction is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

Align the approved destination NAT mapping and corresponding policy with the intended public service. This is a legitimate response to the different issue of Destination NAT and security-policy pair, but it does not correct the specific CSS chassis clustering and failover condition reported. The relevant technical distinction is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

Restore the supported IGMP querier and membership timers on the receiver-facing L3 segment. This is a legitimate response to the different issue of IGMP last-hop membership queries, but it does not correct the specific CSS chassis clustering and failover condition reported. The relevant technical distinction is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

Interfaces with subscribers retain multicast forwarding while pruned branches do not receive sustained data. That observation would support a separate case of PIM-DM flood and prune behavior, not verification of the reported CSS chassis clustering and failover. The relevant observable outcome here is: A member failover preserves approved forwarding and the CSS reports healthy single-system state.

BFD remains stable during normal delay and detects a genuine simulated failure within the approved objective. That observation would support a separate case of BFD detection timers and false alarms, not verification of the reported CSS chassis clustering and failover. The relevant observable outcome here is: A member failover preserves approved forwarding and the CSS reports healthy single-system state.

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 CSS chassis clustering and failover. The relevant observable outcome here is: A member failover preserves approved forwarding and the CSS reports healthy single-system state.

BGP AS_PATH loop detection prevents a route from circulating back through an AS already in its path. This explains BGP AS_PATH loop detection, but not why the issue in this scenario occurs. The specific mechanism is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

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: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

Routing policy can alter selection attributes, but route installation still depends on next-hop reachability. This explains Route-policy next-hop and preference application, but not why the issue in this scenario occurs. The specific mechanism is: CSS coordinates chassis roles and traffic forwarding, but service continuity depends on tested member and link redundancy.

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: Untested clustering can leave a single point of failure despite two physical chassis.

Without membership refresh, valid subscriptions can expire even though PIM backbone forwarding works. This consequence is associated more directly with IGMP last-hop membership queries. For the stated conditions the immediate exposure is: Untested clustering can leave a single point of failure despite two physical chassis.

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: Untested clustering can leave a single point of failure despite two physical chassis.

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 CSS chassis clustering and failover. Begin with: Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover.

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 CSS chassis clustering and failover. Begin with: Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover.

Inspect ip-prefix sequence, mask-length qualifiers and test candidate routes. This check would diagnose Prefix-list network and mask matching, but would not first isolate the described CSS chassis clustering and failover. Begin with: Review CSS roles, health of inter-chassis paths, redundancy alarms and test traffic during failover.