Dimension ES-2008 Ethernet Switch

Chapter 10

Spanning Tree Protocol

This chapter describes the basics and configuration of STP.

10.1 Introduction

Spanning Tree Protocol) is a standardized method (IEEE 802.1D) that eliminates loops in a network by disabling some ports and allowing other ports to forward traffic based on the parameters you configured. STP ensures that there is only one path between a specific source and destination so packets will not travel in loops.

STP provides path redundancy while preventing undesirable loops in the network. STP detects and breaks network loops and provides backup links between switches, bridges or routers. It allows a device to interact with other STP-aware devices in your network to ensure that only one path exists between any two stations on the network.

The root bridge is the base of the spanning tree; it is the bridge with the lowest identifier value (MAC address). Path cost is the cost of transmitting a frame onto a LAN through that port. It is assigned according to the speed of the link to which a port is attached. The slower the media, the higher the cost. Refer to the following table for the recommended path cost (in the allowed range between 1 and 65535) for each link speed.

Table 10-1 Recommended Path Cost

LINK SPEED

RECOMMENDED VALUE

RECOMMENDED RANGE

 

 

 

4Mbps

250

100 to 1000

 

 

 

10Mbps

100

50 to 600

 

 

 

16Mbps

62

40 to 400

 

 

 

100Mbps

19

10 to 60

 

 

 

1Gbps

4

3 to 10

 

 

 

10Gbps

2

1 to 5

 

 

 

On each bridge, the root port is the port through which a bridge communicates with the root. It is the port on this switch with the lowest path cost to the root (the root path cost). If there is no root port, then this switch has been accepted as the root bridge of the spanning tree network.

Spanning Tree Protocol

10-1