Cisco Systems 3750E Specifying the MST Region Configuration and Enabling Mstp, Name name, 19-16

Chapter 19 Configuring MSTP

Configuring MSTP Features

•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. You can achieve load-balancing across a switch stack by manually configuring the path cost.

•All MST boundary ports must be forwarding for load-balancing between a PVST+ and an MST 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 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+ or rapid-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 20-12.

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 only 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
			1-63maps 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.
Step 4	name name		Specify the configuration name. The name string has a maximum length
			of 32 characters and is case sensitive.
		Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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