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Overview

The spanning tree protocol (STP) is a standard Ethernet method for eliminating loops

and providing alternate routes for service protection. Standard STP depends on

information sharing among Ethernet switches/bridges to reconfigure the spanning tree

in the event of a failure. The STP algorithm calculates the best loop-free path

throughout the network.

STP defines a tree that spans all switches in the network; it for example, uses the

capacity of available bandwidth on a link (path cost) to find the optimum tree. It forces

redundant links into a standby (blocked) state. If a link fails or if a STP path cost

changes the STP algorithm reconfigures the spanning tree topology and may reestablish

previously blocked links. The STP also determines one switch that will be the root

switch; all leaves in the spanning tree extend from the root switch.

Maximum bridge diameter

The maximum bridge diameter is the maximum number of bridges between any two

hosts on the bridged LAN for any spanning tree configuration.

For TransLAN

Spanning tree example

The following example network serves to illustrate the principle how a spanning tree is

constructed.

365-312-807R7.2

Issue 4, May 2007

applications the maximum bridge diameter is 25 nodes.

LAN

Switch 2

Switch 1

LAN

Alcatel-Lucent - Proprietary

See notice on first page

Switch 3

LAN

8-45

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Spanning Tree Protocol (Stp) - Alcatel-Lucent 1643 AMS User's Operation Manual