Specifications

CHAPTER

13-1

Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide

78-11380-07

Configuring RSTP and MSTP

This chapter describes how to configure the Cisco implementation of the IEEE 802.1W Rapid Spanning

Tree Protocol (RSTP) and the IEEE 802.1S Multiple STP (MSTP) on your Catalyst 2950 or

Catalyst 2955 switch. It also describes how to configure per-VLAN rapid spanning tree (PVRST). To

use the features described in this chapter, you must have the enhanced software image (EI) installed on

your switch.

RSTP provides rapid convergence of the spanning tree. MSTP, which uses RSTP to provide rapid

convergence, enables VLANs to be grouped into a spanning-tree instance, provides for multiple

forwarding paths for data traffic, and enables load balancing. It improves the fault tolerance of the

network because a failure in one instance (forwarding path) does not affect other instances (forwarding

paths). The most common initial deployment of MSTP and RSTP is in the backbone and distribution

layers of a Layer 2 switched network; this deployment provides the highly-available network required

in a service-provider environment.

Both RSTP and MSTP improve the operation of the spanning tree while maintaining backward

compatibility with equipment that is based on the (original) 802.1D spanning tree, with existing Cisco

per-VLAN spanning tree (PVST), and with the existing Cisco-proprietary Multiple Instance STP

(MISTP). For information about STP, see Chapter 12, “Configuring STP.” For information about

optional spanning-tree features, see Chapter 14, “Configuring Optional Spanning-Tree Features.”

PVRST uses RSTP to provide rapid convergence of spanning-tree instances. PVRST also maintains

backward compatibility with equipment that is based on the 802.1D spanning tree, with PVST and

MISTP. You can use this feature on a switch running MSTP. For information about PVRST, see the

“Spanning-Tree Instances Using RSTP” section on page 13-2.

Note For complete syntax and usage information for the commands used in this chapter, refer to the

command reference for this release.

This chapter consists of these sections:

• Understanding RSTP, page 13-2

• Understanding MSTP, page 13-7

• Interoperability with 802.1D STP, page 13-11

• Configuring RSTP and MSTP Features, page 13-11

• Displaying the MST Configuration and Status, page 13-23