3com WX3000 Manuel D’Utilisation

 

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The term switch used throughout this chapter refers to a switching device in a generic sense or the 
switching engine of a unified switch in the WX3000 series. 

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The sample output information in this manual was created on the WX3024. The output information 
on your device may vary. 

 

Spanning tree protocol (STP) is a protocol conforming to IEEE 802.1d. It aims to eliminate loops on data 
link layer in a local area network (LAN). Devices running this protocol detect loops in the network by 
exchanging packets with one another and eliminate the loops detected by blocking specific ports until 
the 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 and prevents device performance 
degradation. 

Currently, in addition to the protocol conforming to IEEE 802.1d, STP also refers to the protocols based 
on IEEE 802.1d, such as RSTP, and MSTP. 

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:  

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Configuration BPDUs, used to calculate spanning trees and maintain the spanning tree topology.  

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Topology change notification (TCN) BPDUs, used to notify concerned devices of network topology 
changes, if any. 

1)  Root bridge  

A tree network must have a root; hence the concept of “root bridge” has been introduced in STP.  

There is one and only one root bridge in the entire network, and the root bridge can change alone with 
changes of the network topology. Therefore, the root bridge is not fixed.