3Com SuperStack 4 Configuration Manual page 225

10
STP Overview
Implement STP
RSTP C
ONFIGURATION
This chapter covers the following topics:
STP Overview
■
RSTP Configuration
■
RSTP Configuration Example
■
Spanning Tree Protocol (STP) is applied in loop networks to block some undesirable
redundant paths with certain algorithms and prune the network into a loop-free
tree, thereby avoiding the proliferation and infinite cycling of the packet in the
loop network.
The fundamental of STP is that the Switches exchange a special type of protocol
packet (which is called configuration Bridge Protocol Data Units, or BPDU, in IEEE
802.1D) to decide the topology of the network. The configuration BPDU contains
the information enough to ensure the Switches to compute the spanning tree.
The configuration BPDU mainly contains the following information:
1 The root ID consisting of root priority and MAC address
2 The cost of the shortest path to the root
3 Designated bridge ID consisting of designated bridge priority and MAC address
4 Designated port ID consisting of port priority and port number
5 The age of the configuration BPDU: MessageAge
6 The maximum age of the configuration BPDU: MaxAge
7 Configuration BPDU interval: HelloTime
8 Forward delay of the port: ForwardDelay.