Which MSTP-related setting must be identically configured with MSTP to load-balance VLANs on Access-1 switches?

Which MSTP-related setting must be identically configured with MSTP to load-balance VLANs on Access-1 switches?

• A. Spanning-tree bpdu-guard setting
• B. Spanning-tree instance vlan mapping
• C. spanning-tree Cist mapping
• D. spanning-tree root-guard setting

Answer: (B)

In MSTP, traffic for each VLAN is handled by a specific MST instance. To evenly distribute load across multiple links between switches, the mapping of VLANs to MST instances must be the same on all switches in the region. This ensures that the same VLANs take the same relative paths and opportunities for alternative routes, allowing multiple spanning-tree instances to route traffic concurrently rather than funneling all VLANs down a single link. The setting that controls this is the spanning-tree instance to VLAN mapping, which explicitly assigns which VLANs belong to which MST instances. If this mapping differs between Access-1 switches, the network can’t achieve consistent, balanced paths for VLANs, defeating the purpose of MSTP-based load balancing. The other options—bpdu-guard, root-guard, or a CIST mapping—relate to protecting the topology or to the internal spanning tree structure, not to how VLANs are distributed across MST instances for load balancing.

In MSTP, traffic for each VLAN is handled by a specific MST instance. To evenly distribute load across multiple links between switches, the mapping of VLANs to MST instances must be the same on all switches in the region. This ensures that the same VLANs take the same relative paths and opportunities for alternative routes, allowing multiple spanning-tree instances to route traffic concurrently rather than funneling all VLANs down a single link. The setting that controls this is the spanning-tree instance to VLAN mapping, which explicitly assigns which VLANs belong to which MST instances. If this mapping differs between Access-1 switches, the network can’t achieve consistent, balanced paths for VLANs, defeating the purpose of MSTP-based load balancing. The other options—bpdu-guard, root-guard, or a CIST mapping—relate to protecting the topology or to the internal spanning tree structure, not to how VLANs are distributed across MST instances for load balancing.