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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter15 Configuring MSTP Configuring MSTP Features
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 within the MST cloud than a pa th th rou gh the PVST+ o r ra pid- 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.
•For configuration guidelines about UplinkFast, BackboneFast, and cross-stack UplinkFast, see the
“Optional Spanning-Tree Configuration Guidelines” section on page 16-13.
Specifying the MST Region Configuration and Enabling MSTP
For two or more switches to be in the same MST region, they must have the same VLAN-to-instance
mapping, the same configuration revision number, and the same name.
A region can have one member or multiple members with the sam e M ST co nfigurat ion; ea c h m embe r
must be capable of processing RSTP BPDUs. There is no limit t o the numb er of MS T regi on s in a
network, but each region can support up to 16 spanning-tree instances. You can assign a VLAN to only
one spanning-tree instance at a time.
Beginning in privileged EXEC mode, follow these steps to specify the MST region configuration and
enable MSTP. This procedure is required.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree mst configuration Enter MST configuration mode.
Step3 instance instance-id vlan vlan-range Map VLANs to an MST instance.
•For instance-id, you can specify a single instance, a range of
instances separated by a hyphen, or a series of instances separated by
a comma. The range is 1 to 15.
•For vlan vlan-range, the range is 1 to 1005 when the SI is installed
and 1 to 4094 when the EI is installed.
When you map VLANs to an MST instance, the mapping is incremental,
and the VLANs specified in the command are added to or removed from
the VLANs that were previously mapped.
To specify a VLAN range, use a hyphen; for example, instance 1 vlan
1-63 maps VLANs 1 through 63 to MST instance 1.
To specify a VLAN series, use a comma; for example, instance 1 vlan 10,
20, 30 maps VLANs 10, 20, and 30 to MST instance 1.
Step4 name name Specify the configuration name. The name string has a maximum length
of 32 characters and is case sensitive.
Step5 revision version Specify the configuration revision number. The range is 0 to 65535.
Step6 show pending Verify your configuration by displaying the pending configuration.
Step7 exit Apply all changes, and return to global configuration mode.