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12-12
Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 12 Configuring RSTP and MSTP
Configuring RSTP and MSTP Features
Default RSTP and MSTP Configuration
Table 12-3 shows the default RSTP and MSTP configuration.
RSTP and MSTP Configuration Guidelines
These are the configuration guidelines for RSTP and MSTP:
• The UplinkFast, BackboneFast, and cross-stack UplinkFast features are not supported with the
RSTP and MSTP.
• Per-VLAN RSTP is not supported. When you enable MST by using the spanning-tree mode mst
global configuration command, RSTP is enabled.
• PVST, PVST+ and MSTP are supported, but only one version can be active at any time; all VLANs
run PVST, or all VLANs run MSTP.
• 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.
• All MST boundary ports must be forwarding for load balancing between a PVST+ and an MST
cloud. For this to happen, 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 of the MST regions must contain the CST root,
and all of the other MST regions must have a better path to the root contained with the MST cloud
than a path through the PVST+ cloud. You might have to manually configure the switches in the
clouds.
• Partitioning the network into a large number of regions is not recommended. However, if this
situation is unavoidable, we recommend that you partition the switched LAN into smaller LANs
interconnected by routers or non-Layer 2 devices.
Table 12-3 Default RSTP and MSTP Configuration
Feature Default Setting
Spanning-tree mode PVST (MSTP and RSTP 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.