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Multiple Spanning-Tree Protocol-802.1Q-2005
- Removes tie between VLANs and Spanning-Tree instances.
- Needed when reaching the max limit of VLANs, because the switch will not support that many STP instances.
- MST Region:
- Bridges that all agree upon instance name, revision number, and VLAN to STP instance mappings.
- Intra Region
- Within Region, details are known.
- VLAN to STPIs are manually defined.
- Undefined VLANs fall into CIST/MST0
- Inter Region
- Information between regions is not known.
- Regions see each other as virtual bridges.
- Simplifies Inter-Region calculation.
- Intra-Region MSTIs collapsed into CIST.
- Configuration:
- Requires Region name, Revision Number, VLAN to instance mapping
- Enable MST globally.
- Commands:
- ‘spanning-tree mst <instance> priority’
- ‘spanning-tree mst <instance> root <primary/secondary>’
- ‘show spanning-tree mst <instance>’
- ‘show spanning-tree root’
- Enabling:
- ‘spanning-tree mode mst’
- ‘spanning-tree mst configuration’
- ‘name REGION0’
- ‘instance 1 vlan 1-10’
- ‘instance 2 vlan 11-20’
- The root bridge must be in the MST instance, otherwise instance will fail.
- Backwards Compatibility:
- When running RSTP or PVST alongside MST, a show spanning-tree will provide ‘Bound’ ports.
- Ports Gi0/3 and Gi1/0 are connected to a device running PVST. This works though because the root bridge for VLAN 10 is in the MST region.
- All commands are the same when using RSTP and MST, but instead of using ‘vlan’, we use ‘mst’ and region number/name.
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