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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter15 Configuring MSTP
Configuring MSTP Features
Default MSTP Configuration
Table15-3 shows the de fault M ST P configur ation .
For information about the supported number of spanning-tree instances, see the “Supported
Spanning-Tree Instances” section on page 14-9.
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. Per-VLAN RSTP is not supported in software rel e ases earlier than Cisco
IOS Release 12.1(13)EA1.
•For two or more switches to be in the same MST region, they must have the same VLA N-to-instance
map, the same configuration revision number, and the same name.
•The switch 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 VL ANs run MSTP.) For more
information, see the “Spanning-Tree Interoperability and Backward Compatibility” section on
page 14-10.
•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 map ping) o n e ach
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, a ll V LAN -to- inst ance mapping
assignments must match; otherwise, all traffic flows on a single link.
•All MST boundary ports must be forwarding for load balancing be twee n a PVST + a nd an M ST
cloud or between a rapid-PVST+ and an MST cloud. For this to occur, the IST master of the MST
cloud should also be the root of the CST. If the MST cloud consists of multiple MST regions, one
Table15-3 Default MSTP Configuration
Feature Default Setting
Spanning-tree mode PVST+ (Rapid PVST+ and MSTP are disabled).
Switch priority (configurable on a per-CIST interface basis) 32768.
Spanning-tree port priority (configurable on a per-CIST interface basis) 128.
Spanning-tree port cost (configurable on a per-CIST interface 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.