
17-12
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-09
Chapter 17 Configuring MSTP
Configuring MSTP Features
Default MSTP Configuration
shows the default MSTP configuration.
For information about the supported number of spanning-tree instances, see the
Spanning-Tree Instances” section on page 16-9
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 releases 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 VLAN-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.
•
The UplinkFast, BackboneFast, and cross-stack UplinkFast features are not supported with the
MSTP.
•
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
. For information on the recommended trunk port configuration, see the
Other Features” section on page 12-19
•
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.
Table 17-3
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.