Huawei quidway s7700 - MSTP Overview; MSTP Introduction

9.1 MSTP Overview
MSTP enables multiple VLANs to be grouped into a spanning-tree instance, forming a VLAN
mapping table. Each instance has a spanning-tree topology independent of other spanning-tree
instances. This architecture provides multiple forwarding paths for data traffic and enables load
balancing.
9.1.1 MSTP Introduction
The Multiple Spanning Tree Protocol (MSTP) incorporates the functions of the Spanning Tree
Protocol (STP) and Rapid Spanning Tree Protocol (RSTP), and outperforms them. It enables
rapid convergence and provides load balancing across redundant paths.
Background
STP and RSTP are used in a LAN to prevent loops. The devices running STP/RSTP discover
loops on the network by exchanging information with each other and trim the ring topology into
a loop-free tree topology by blocking a certain interface. Replication and circular propagation
of packets are thus prevented on the network and the processing performance of devices is
improved by avoiding repeated packets on the network.
STP and RSTP both have a defect: All VLANs on a LAN use one spanning tree, and thus inter-
VLAN load balancing cannot be performed. Once a link is blocked, the link will no longer
transmit traffic, wasting bandwidth and causing a failure in forwarding certain VLAN packets.
To fix the defect of STP and RSTP, the IEEE released the 802.1s standard in 2002, defining
MSTP. MSTP compatible with STP and RSTP implements rapid convergence and provides
multiple paths to load balance VLAN traffic.
Table 9-1 shows the comparison between STP, RSTP, and MSTP.
Quidway S7700 Smart Routing Switch
Configuration Guide - Ethernet 9 MSTP Configuration
Issue 01 (2011-07-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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