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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring MSTP
Configuring MSTP Features
For information about the supported number of spanning-tree instances, see the “Supported
Spanning-Tree Instances” section on page 1-10.
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 Catalyst 3560-X 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.
• For two or more stacked Catalyst 3750-X 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 Catalyst 3560-X switch supports up to 65 MST instances. The number of VLANs that can be
mapped to a particular MST instance is unlimited.
• The Catalyst 3750-X switch stack supports up to 65 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 1-11. For information on the recommended trunk port configuration, see the “Interaction with
Other Features” section on page 1-18.
• 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 1-11.
• 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.
• For load-balancing across redundant paths in the network to work, all VLAN-to-instance mapping
assignments must match; otherwise, all traffic flows on a single link. You can achieve
load-balancing across a switch stack by manually configuring the path cost.
Spanning-tree port priority (configurable on a per-CIST port basis) 128.
Spanning-tree port cost (configurable on a per-CIST port basis) 1000 Mb/s: 4.
100 Mb/s: 19.
10 Mb/s: 100.
Hello time 2 seconds.
Forward-delay time 15 seconds.
Maximum-aging time 20 seconds.
Maximum hop count 20 hops.
Table 1-4 Default MSTP Configuration (continued)
Feature Default Setting
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