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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration 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 14-10.
MSTP Configuration Guidelines
These are the configuration guidelines for MSTP:
•MSTP is supported only on NNIs on the switch. UNIs do not participate in MSTP.
•When you enable MST by using the spanning-tree mode mst global configuration command, RSTP
is automatically enabled.
•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 VLA Ns run MSTP.) For more
information, see the “Spanning-Tree Interoperability and Backward Compatibility” section on
page 14-10. For information on the recommended trunk port configuration, see the “Interaction with
Other Features” section on page 11-16.
•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, 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 Rapid PVST+ (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.