Spanning TreeMST Config

name [region-name]

Configures the Multiple Spanning Tree (MST) region name, which is required to group switches into the same MST region for interoperable MSTP operation.

Syntax·MST Config

name [region-name]

When to Use This Command

When deploying MSTP in a campus network to define a consistent region name across all switches in the same MST region.
When migrating from Rapid PVST+ to MSTP to ensure all switches in the region share the same name and revision number.
When adding a new switch to an existing MST region, you must configure the same region name to avoid topology instability.
When troubleshooting MST region mismatches that cause spanning tree loops or blocked ports.

Command Examples

Configuring MST region name

name CAMPUS_CORE

This command sets the MST region name to 'CAMPUS_CORE'. The name is case-sensitive and must match exactly on all switches in the same region. No output is generated upon successful configuration.

Verifying MST region configuration

show spanning-tree mst configuration

Name      [CAMPUS_CORE]
Revision  1     Instances configured 2
Instance  Vlans mapped
--------  ---------------------------------------------------------------------
0         1-9,11-99,101-199,201-4094
1         10,100,200

The output shows the configured MST region name 'CAMPUS_CORE', revision number (default 1), and the VLAN-to-instance mapping. Ensure the name matches other switches in the region.

Understanding the Output

The 'show spanning-tree mst configuration' command displays the MST region configuration. The 'Name' field shows the configured region name; it must be identical on all switches in the same MST region. The 'Revision' field is a number (0-65535) that must also match across the region. The 'Instances configured' shows how many MST instances are active. The table lists each MST instance and the VLANs mapped to it. A mismatch in region name or revision will cause the switch to consider itself in a different region, leading to boundary ports and potential loops.

CCNA Exam Tips

CCNA 200-301 exam expects you to know that MST region name, revision number, and VLAN-to-instance mapping must match on all switches in the same MST region.

A common exam scenario: two switches with different MST region names will treat the link as an MST boundary, reverting to PVST+ behavior on that port.

The 'name' command is configured in MST configuration mode, entered via 'spanning-tree mst configuration'.

Remember that the MST region name is case-sensitive and can be up to 32 characters.

Common Mistakes

Typing the region name with a typo or different case on different switches, causing them to be in different regions.

Forgetting to also set the revision number to match; the default revision is 1, but if one switch has a different revision, they will not form a single region.

Configuring the region name but not applying the configuration with 'exit' or 'end' to activate it.

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