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.

Published by Yup2k