Chapter 19
Configuring Standard-Compliant IEEE MST
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Specifying the MST Region Configuration and Enabling MST
For two or more routers to be in the same MST region, they must have the same VLAN-to-instance
mapping, the same configuration revision number, and the same MST name.
A region can have one member or multiple members with the same MST configuration; each member
must be capable of processing RSTP BPDUs. There is no limit to the number of MST regions in a
network, but each region can only support up to 65 spanning tree instances. You can assign a VLAN to
only one spanning tree instance at a time.
To specify the MST region configuration and enable MST, perform this task:
Command
Step 1
Router# configure terminal
Step 2
Router(config)# spanning-tree mst configuration
Step 3
Router(config-mst)# instance instance_id vlan
vlan_range
Step 4
Router(config-mst)# name instance_name
Step 5
Router(config-mst)# revision version
Step 6
Router(config-mst)# show pending
Step 7
Router(config)# exit
OL-4266-08
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 non-Layer 2 devices.
Adding or removing VLANs to an existing MST instance will trigger spanning tree recalculation for
that MST instance, and the traffic of all the VLANs for that MST instance will be disrupted.
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
Purpose
Enters global configuration mode.
Enters MST configuration mode.
Maps VLANs to an MST instance.
For instance_id, the range is 0 to 4094.
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For vlan vlan_range, the range is 1 to 4094.
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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.
Specifies the instance name. The name string has a
maximum length of 32 characters and is case sensitive.
Specifies the configuration revision number. The range is
0 to 65535.
Verifies your configuration by displaying the pending
configuration.
Applies all changes, and return to global configuration
mode.
Configuring MST
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