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MSTP CONFIGURATION
When configuring MSTP, go to these sections for information you are interested
in:
■ “MSTP Overview” on page 197
■ “Configuring the Root Bridge” on page 213
■ “Configuring Leaf Nodes” on page 224
■ “Performing mCheck” on page 228
■ “Configuring Protection Functions” on page 233
■ “Displaying and Maintaining MSTP” on page 235
MSTP Overview
Introduction to STP Why STP?
The Spanning Tree Protocol (STP) was established based on the 802.1d standard of
IEEE to eliminate physical loops at the data link layer in a local area network (LAN).
Devices running this protocol detect loops in the network by exchanging
information with one another and eliminate loops by selectively blocking certain
ports until the loop structure is pruned into a loop-free network structure. This
avoids proliferation and infinite recycling of packets that would occur in a loop
network and prevents deterioration of the packet processing capability of network
devices caused by duplicate packets received.
In the narrow sense, STP refers to the STP protocol defined in IEEE 802.1d; in the
broad sense, it refers to the STP protocol defined in IEEE 802.1d and various
enhanced spanning tree protocols derived from the STP protocol.
Protocol Packets of STP
STP uses bridge protocol data units (BPDUs), also known as configuration
messages, as its protocol packets.
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 calculation.
In STP, BPDUs come in two types:
■ Configuration BPDUs, used for calculating spanning trees and maintaining the
spanning tree topology.
■ Topology change notification (TCN) BPDUs, used for notifying concerned
devices of network topology changes, if any.
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