3Com Switch 8800 Advanced Software V5 Configuration Guide

11
MSTP CONFIGURATION
When configuring MSTP, go to these sections for information you are interested
in:
■ “MSTP Overview” on page 93
■ “Configuration Task List” on page 107
■ “Configuring the Root Bridge” on page 109
■ “Configuring Leaf Nodes” on page 120
■ “Performing mCheck” on page 124
■ “Configuring the VLAN Ignore Feature” on page 125
■ “Configuring Digest Snooping” on page 126
■ “Configuring No Agreement Check” on page 128
■ “Configuring Protection Functions” on page 130
■ “Displaying and Maintaining MSTP” on page 134
■ “MSTP Configuration Examples” on page 134
MSTP Overview
Introduction to STP Functions of STP
Spanning tree protocol (STP) aims to eliminate loops in a local area network (LAN).
Devices running this protocol detect loops in the network by exchanging
information with one another and eliminate the loops detected by blocking
certain ports until the loop network is pruned into one with tree topology. As a
network with tree topology is loop-free, it prevents packets in it from being
duplicated and forwarded endlessly.
Protocol packets of STP
STP uses bridge protocol data units (BPDUs) for exchanging information. BPDU is
also known as configuration packets (messages).
STP identifies the network topology by transmitting BPDUs between STP compliant
network devices. BPDUs contain sufficient information for the network devices to
complete the spanning tree computing.
In STP, BPDUs come in two types:
■ Configuration BPDUs, used to maintain the spanning tree topology.
■ Topology change notification (TCN) BPDUs, used to notify concerned devices of
network topology changes, if any.