Enterasys Networks VH-2402S ユーザーズマニュアル

88  Spanning Tree Concepts

VH-2402S

When the Spanning Tree Protocol is enabled for the first time or when 
there is a change in the network topology, such as a failure or the addition 

or removal of a component, the Spanning Tree Protocol automatically 

sets up the active topology of the current network.

Periodically, all devices running the Spanning Tree Protocol on a network 

transmit packets to each other “in care of” the Bridge Group Address 

which all bridges share. When a bridge receives a frame sent to the 
Bridge Group Address, the bridge’s Spanning Tree Protocol processes 

the packet. Application software and other LAN segments ignore the 

packet. Bridges communicate between each other in order to determine 
the Root Bridge.

During communication between bridges, one bridge is determined to 

have the lowest bridge identifier. This bridge becomes the Root Bridge. 

After the Root Bridge has been selected, each LAN segment looks for the 

bridge that has the lowest cost relative to the Root Bridge. These bridges 

become Designated Bridges.

Each Designated Bridge selects a Designated Port. This port is 

responsible for forwarding packets to the Root Bridge. 

When the active topology of the network is determined, all packets 
between any two nodes in the network use only one path. Where a 

duplicate path exists, the non-designated port is put into a blocking state. 

If there is a change in the network topology due to a failure or the removal 
or addition of any active components, the active topology also changes. 

This may trigger a change in the state of some blocked ports.