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That option concerns RSTP port roles and rapid convergence. That follows from the targeted action: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume.

That option concerns OSPF interface security and passive network advertisement. That follows from the targeted action: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume.

That option concerns Switch stacking clustering and split-brain risk. That follows from the targeted action: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume.

This option proposes: Declare a two-switch stack fully protected against dual-active behavior simply because both chassis still have electrical power. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (A newly installed access switch unexpectedly becomes root after receiving a lower bridge-priority configuration than the designed aggregation switches.).

This option proposes: Change an MST instance's VLAN mapping on one switch only and assume adjacent switches will continue to recognize exactly the same MST region. It addresses the different topic MSTP region and VLAN-to-instance mappings, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (A newly installed access switch unexpectedly becomes root after receiving a lower bridge-priority configuration than the designed aggregation switches.).

This option proposes: Assume a configured BFD transmit interval alone exactly equals the detection timeout regardless of the peer's receive requirement or detection multiplier. It addresses the different topic BFD detection multiplier and negotiated timers, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (A newly installed access switch unexpectedly becomes root after receiving a lower bridge-priority configuration than the designed aggregation switches.).

This option proposes: Diagnose RSTP forwarding state by identifying root, designated and alternate ports and the topology's point-to-point characteristics. It addresses the different topic RSTP port roles and rapid convergence, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Inspect compatible IS-IS NET area IDs, interface levels and authentication before changing a routing process after adjacency failure. It addresses the different topic IS-IS area addresses and adjacency prerequisites, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Validate physical stack links, member roles and split-brain safeguards before considering a multi-switch logical chassis redundant. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Stacked switches can operate as a single logical device only while the supported control and data channels are consistent; a partition without dual-active detection risks conflicting forwarding or management identities. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: BFD failure detection depends on negotiated receive intervals and a multiplier, so unrealistically aggressive values can cause transient congestion or scheduler delays to trigger unnecessary session-down events. It addresses the different topic BFD detection multiplier and negotiated timers, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Rapid Spanning Tree Protocol reduces convergence time by exchanging proposal/agreement information on eligible links and maintaining alternate paths, while only the root and designated forwarding ports should carry traffic in a stable tree. It addresses the different topic RSTP port roles and rapid convergence, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Inspect the active RIB prefix and mask, BGP network or import-route configuration, route-policy matches and outbound Adj-RIB-Out to the peer. It addresses the different topic BGP route origin network and redistribution policy, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Inspect bridge IDs, selected root bridge, root-path costs, each port role and current alternate/discarding state. It addresses the different topic RSTP port roles and rapid convergence, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Compare MST region name, revision, VLAN-instance tables, region digest and root bridge per instance on neighboring switches. It addresses the different topic MSTP region and VLAN-to-instance mappings, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

That option concerns Switch stacking clustering and split-brain risk. That follows from the targeted Recommended action: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume.

That option concerns WLAN VLAN pools and DHCP address scopes. That follows from the targeted Recommended action: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume.

That option concerns MSTP region and VLAN-to-instance mappings. That follows from the targeted Recommended action: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume.

This option proposes: Change an MST instance's VLAN mapping on one switch only and assume adjacent switches will continue to recognize exactly the same MST region. It addresses the different topic MSTP region and VLAN-to-instance mappings, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Declare a two-switch stack fully protected against dual-active behavior simply because both chassis still have electrical power. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: State that BGP must always choose the route with the fewest autonomous systems even when the local operator configured a stronger valid preference. It addresses the different topic BGP route preference sequence and policy precedence, not the directly tested RSTP designated root and backup topology selection failure in the stated incident (Two redundant switches appear equal in topology depth, and engineers need to explain why one interface is designated and another becomes alternate.).

This option proposes: Validate physical stack links, member roles and split-brain safeguards before considering a multi-switch logical chassis redundant. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: Select and verify a suitable root bridge for a switched domain without relying on arbitrary port names or traffic volume. It addresses the different topic RSTP designated root and backup topology selection, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: Use AS_PATH to reason about external route propagation, loop prevention and intentional prepending effects. It addresses the different topic BGP AS_PATH path-vector loop prevention, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: Passive OSPF interfaces can stop unwanted neighbor discovery while their connected networks may still be advertised through the OSPF process; authentication protects routing exchanges and requires compatible peer settings. It addresses the different topic OSPF interface security and passive network advertisement, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: STP and RSTP root election depends on bridge IDs and configured priorities, while root-path cost and port IDs help select forwarding roles; a device with more physical connections is not automatically elected root. It addresses the different topic RSTP designated root and backup topology selection, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: Stacked switches can operate as a single logical device only while the supported control and data channels are consistent; a partition without dual-active detection risks conflicting forwarding or management identities. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: Inspect member and master status, stack-link connectivity, dual-active detection mechanisms and forwarding after an isolated partition test. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

This option proposes: Compare received iBGP routes to the same prefix, LOCAL_PREF values, policy application points and next-hop reachability across edge routers. It addresses the different topic BGP LOCAL_PREF within one autonomous system, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.). The better discriminating check for this case is: Compare MST region name, revision, VLAN-instance tables, region digest and root bridge per instance on neighboring switches. The targeted correction is: Ensure consistent MST region name, revision and VLAN-to-instance mapping before expecting switches to share the same spanning-tree instance topology.

This option proposes: Inspect bridge IDs, selected root bridge, root-path costs, each port role and current alternate/discarding state. It addresses the different topic RSTP port roles and rapid convergence, not the directly tested MSTP region and VLAN-to-instance mappings failure in the stated incident (Campus access switches were configured with identical MST region names but different VLAN mappings, creating a boundary where the designer expected one region.).

That option concerns Route redistribution feedback loops and route tags. That follows from the targeted action: Ensure consistent MST region name, revision and VLAN-to-instance mapping before expecting switches to share the same spanning-tree instance topology.

That option concerns Switch stacking clustering and split-brain risk. That follows from the targeted action: Ensure consistent MST region name, revision and VLAN-to-instance mapping before expecting switches to share the same spanning-tree instance topology.

That option concerns RSTP port roles and rapid convergence. That follows from the targeted action: Ensure consistent MST region name, revision and VLAN-to-instance mapping before expecting switches to share the same spanning-tree instance topology.