How Stp Works; Initialization - 3Com 9000 SX User Manual

How STP Works

If the link through Bridge C fails, as shown in Figure 7-3, the STP
system reconfigures the network so that traffic from segment 2 flows
through Bridge B.
Figure 7-3 Traffic flowing through Bridge B
STP has the following three stages of operation:

Initialization

Stabilization
Reconfiguration
Initialization
Initially, the STP system requires the following before it can configure
the network:
All bridges exchange information by way of Bridge Protocol Data
Units (BPDUs), which are transmitted in packets with a known
multicast address
To determine a single root bridge as a result of BPDU exchange
The Root Bridge is selected on the basis of it having the lowest Bridge
Identifier value. This value is a combination of the unique MAC address
of the bridge and a priority component defined for the bridge.
Overview of the Spanning Tree Protocol 7-3