ES-2048 User’s Guide

CHAPTER 11

Spanning Tree Protocol

The switch supports Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP) as defined in the following standards.

•IEEE 802.1D Spanning Tree Protocol

•IEEE 802.1w Rapid Spanning Tree Protocol

Note: In this user’s guide, “STP” refers to both STP and RSTP.

11.1 STP/RSTP Overview

(R)STP detects and breaks network loops and provides backup links between switches, bridges or routers. It allows a switch to interact with other (R)STP -compliant switches in your network to ensure that only one path exists between any two stations on the network.

The switch uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allows faster convergence of the spanning tree than STP (while also being backwards compatible with STP- only aware bridges). In RSTP, topology change information is directly propagated throughout the network from the device that generates the topology change. In STP, a longer delay is required as the device that causes a topology change first notifies the root bridge that then notifies the network. Both RSTP and STP flush unwanted learned addresses from the filtering database. In RSTP, the port states are Discarding, Learning, and Forwarding.

Note: In this user’s guide, “STP” refers to both STP and RSTP.

11.1.1 STP Terminology

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.

Table 22 STP Path Costs

 

LINK SPEED

RECOMMENDED VALUE

RECOMMENDED

ALLOWED RANGE

 

 

 

RANGE

 

Path Cost

4Mbps

250

100 to 1000

1 to 65535

 

 

 

 

 

Path Cost

10Mbps

100

50 to 600

1 to 65535

 

 

 

 

 

Chapter 11 Spanning Tree Protocol

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