Chapter 15 Configuring Mstp - Cisco Catalyst 3750 Software Configuration Manual

Metro switch

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Configuring MSTP

This chapter describes how to configure the Cisco implementation of the IEEE 802.1s Multiple STP

(MSTP) on the Catalyst 3750 Metro switch.

The MSTP enables multiple VLANs to be mapped to the same spanning-tree instance, thereby reducing

the number of spanning-tree instances needed to support a large number of VLANs. The MSTP 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 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.

When the switch is in the multiple spanning-tree (MST) mode, the Rapid Spanning Tree Protocol

(RSTP), which is based on IEEE 802.1w, is automatically enabled. The RSTP provides rapid

convergence of the spanning tree through explicit handshaking that eliminates the IEEE 802.1D

forwarding delay and quickly transitions root ports and designated ports to the forwarding state.

Both MSTP and RSTP improve the spanning-tree operation and maintain backward compatibility with

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

Instance STP (MISTP), and with existing Cisco per-VLAN spanning-tree plus (PVST+) and rapid

per-VLAN spanning-tree plus (rapid PVST+). For information about PVST+ and rapid PVST+, see

Chapter 14, "Configuring STP."

UplinkFast, root guard, and so forth, see

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 MSTP, page 15-2

Understanding RSTP, page 15-6

Configuring MSTP Features, page 15-11

Displaying the MST Configuration and Status, page 15-23

For information about other spanning-tree features such as Port Fast,

Chapter 16, "Configuring Optional Spanning-Tree Features."

Catalyst 3750 Metro Switch Software Configuration Guide

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