18-13
Catalyst 3750 Switch Software Configuration Guide
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Chapter 18 Configuring MSTP
Configuring MSTP Features
Default MSTP Configuration
Table 18-3 shows the default MSTP configuration.
For information about the supported number of spanning-tree instances, see the “Supported
Spanning-Tree Instances” section on page 17-10.
MSTP Configuration Guidelines
These are the configuration guidelines for MSTP:
• When you enable MST by using the spanning-tree mode mst global configuration command, RSTP
is automatically enabled.
• For two or more stacked switches to be in the same MST region, they must have the same
VLAN-to-instance map, the same configuration revision number, and the same name.
• The switch stack supports up to 16 MST instances. The number of VLANs that can be mapped to a
particular MST instance is unlimited.
• PVST+, rapid PVST+, and MSTP are supported, but only one version can be active at any time. (For
example, all VLANs run PVST+, all VLANs run rapid PVST+, or all VLANs run MSTP.) For more
information, see the “Spanning-Tree Interoperability and Backward Compatibility” section on
page 17-11. For information on the recommended trunk port configuration, see the “Interaction with
Other Features” section on page 13-20.
• All stack members run the same version of spanning tree (all PVST+, rapid PVST+, or MSTP). For
more information, see the “Spanning-Tree Interoperability and Backward Compatibility” section on
page 17-11.
• VTP propagation of the MST configuration is not supported. However, you can manually configure
the MST configuration (region name, revision number, and VLAN-to-instance mapping) on each
switch within the MST region by using the command-line interface (CLI) or through the SNMP
support.
Table 18-3 Default MSTP Configuration
Feature Default Setting
Spanning-tree mode PVST+ (Rapid PVST+ and MSTP are disabled).
Switch priority (configurable on a per-CIST port basis) 32768.
Spanning-tree port priority (configurable on a per-CIST port basis) 128.
Spanning-tree port cost (configurable on a per-CIST port basis) 1000 Mbps: 4.
100 Mbps: 19.
10 Mbps: 100.
Hello time 2 seconds.
Forward-delay time 15 seconds.
Maximum-aging time 20 seconds.
Maximum hop count 20 hops.
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