CHAPTER
15-1
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
15
Understanding and Configuring Multiple Spanning Trees
This chapter describes how to configure the IEEE 802.1s Multiple Spanning Tree (MST) protocol on the
Catalyst 4500 series switch. MST is a new IEEE standard derived from Cisco's proprietary
Multi-Instance Spanning-Tree Protocol (MISTP) implementation. With MST, you can map a single
spanning-tree instance to several VLANs.
This chapter includes the following major sections:
Overview of MST, page 15-1
MST Configuration Restrictions and Guidelines, page 15-8
Configuring MST, page 15-9
Note For complete syntax and usage information for the switch commands used in this chapter, refer to the
Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm.

Overview of MST

The following sections describe how MST works on a Catalyst 4500 series switch:
IEEE 802.1s MST, page 15-2
IEEE 802.1w RSTP, page 15-3
MST-to-SST Interoperability, page 15-4
Common Spanning Tree, page 15-5
MST Instances, page 15-5
MST Configuration Parameters, page 15-5
MST Regions, page 15-6
Message Age and Hop Count, page 15-7
MST-to-PVST+ Interoperability, page 15-8