Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 10 Configuring MSTP
Configuring MSTP Features
• PVST+ and MSTP are supported, but only one version can be active at any time. (For example, all
VLANs run PVST+ or all VLANs run MSTP.) For more information, see the “Spanning-Tree
Interoperability and Backward Compatibility” section on page 9-10. For information on the
recommended trunk port configuration, see the “Interaction with Other Features” section on
page 7-13.
• 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).
• 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 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 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 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.
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 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 support up to 65 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
Step 1
configure terminal Enter global configuration mode.
Step 2
spanning-tree mst configuration Enter MST configuration mode.
Step 3
instance instance-id vlan vlan-range Map VLANs to an MST instance.
• For instance-id, the range is 0 to 4094.
• For vlan vlan-range, the range is 1 to 4094.
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.