Cisco Catalyst 2960 Series, Configuration Manual

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• For load-balancing between a per-VLAN spanning tree plus (PVST+) and an MST cloud or between a
rapid-PVST+ and an MST cloud to work, all MST boundary ports must be forwarding. MST boundary
ports are forwarding when the internal spanning tree (IST) master of the MST cloud is the root of the
common spanning tree (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.
Related Topics
Specifying the MST Region Configuration and Enabling MSTP , on page 261
MSTP Configuration Guidelines, on page 243
Multiple Spanning-Tree Regions, on page 245
Restrictions for MSTP
• The switch stack supports up to 65 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 VLANs run MSTP.)
• All stack members must run the same version of spanning tree (all PVST+, Rapid PVST+, or MSTP).
• VLAN Trunking Protocol (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 Simple Network Management Protocol (SNMP) support.
• 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.
• A region can have one member or multiple members with the same MST configuration; each member
must be capable of processing rapid spanning tree protocol (RSTP) Bridge Protocol Data Units (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.
• After configuring a switch as the root switch, we recommend that you avoid manually configuring the
hello time, forward-delay time, and maximum-age time through the
spanning-tree mst hello-time ,
spanning-tree mst forward-time , and the spanning-tree mst max-age global configuration commands.
Table 29: PVST+, MSTP, and Rapid PVST+ Interoperability and Compatibility
Rapid PVST+ MSTP PVST+
Yes (reverts to PVST+) Yes (with restrictions) Yes PVST+
Yes (reverts to PVST+) Yes Yes (with restrictions) MSTP
Yes Yes (reverts to PVST+) Yes (reverts to PVST+) Rapid PVST+
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
242
Restrictions for MSTP