Huawei AR3200 Series, Configuration Manual - Lan

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8.1 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. Devices can run STP to discover loops on
the network by exchanging information with each other, and trim the ring topology into a loop-
free tree topology by blocking an interface. These capabilities help prevent replication and
circular propagation of packets on the network which in turn helps avoid degradation of
switching device performance.
STP and RSTP share a similar limitation: All VLANs on a LAN use one spanning tree, which
means that inter-VLAN load balancing cannot be performed. A link will no longer transmit
traffic once it is blocked, which wastes bandwidth and causes forwarding failures in some
VLANs.
To address the deficiencies in STP and RSTP, the IEEE released the 802.1s standard in 2002,
which defines MSTP. MSTP is compatible with STP and RSTP. It implements rapid
convergence and provides multiple paths to load balance VLAN traffic.
Table 8-1 compares STP, RSTP, and MSTP in terms of the characteristics of each protocol and
their applicable environments.
Table 8-1 Comparison between STP, RSTP, and MSTP
Spanning Tree
Protocols Characteristics Application
Scenarios Precautions
STP Ensures a loop-free tree
topology that helps prevent
broadcast storms and allows
for redundant links between
switches. Irrespective of
users or services,
all VLANs share
one spanning tree. l If the current
switching
device
supports only
STP, STP is
recommende
d. For details,
see
STP/
RSTP
Configurati
on
.
l If the current
switching
device
supports both
STP and
RSTP, RSTP
is
recommende
d. For details,
RSTP l Ensures a loop-free tree
topology that helps
prevent broadcast storms
and allows for redundant
links between switches.
l Provides a feedback
mechanism to confirm
topology convergence,
implementing rapid
convergence.
Huawei AR3200 Series Enterprise Routers
Configuration Guide - LAN
8 MSTP Configuration
Issue 02 (2012-03-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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