User Manual User guide

Rockwell Automation Publication 1783-UM006A-EN-P - May 2014 301

Chapter 9

Configuring Spanning Tree Protocol

This chapter describes how to configure Spanning Tree Protocol (STP) on your

access point.

Understanding Spanning

Tree Protocol (STP)

STP is a Layer 2 link management protocol that provides path redundancy while

preventing loops in the network. For a Layer 2 Ethernet network to function

properly, one active path can only exist between any two stations. Spanning-tree

operation is transparent to end stations, that cannot detect whether they are

connected to a single LAN segment or to a LAN of multiple segments.

When you create fault-tolerant internet-works, you must have a loop-free path

between all nodes in a network. The spanning-tree algorithm calculates the best

loop-free path throughout a Layer 2 network. Infrastructure devices such as

wireless access points and switches send and receive spanning-tree frames, called

bridge protocol data units (BPDUs), at regular intervals. The devices don’t

forward these frames but use them to construct a loop-free path.

Multiple active paths among end stations cause loops in the network. If a loop

exists in the network, end stations can receive duplicate messages. Infrastructure

devices can also learn end-station MAC addresses on multiple Layer 2 interfaces.

These conditions result in an unstable network.

Topic Page

Understanding Spanning Tree Protocol (STP) 301

Access Point/Bridge Protocol Data Units 302

Election of the Spanning-tree Root 304

Spanning-tree Timers 304

Creating the Spanning-tree Topology 305

Configuring STP Features 308

STP Configuration Examples 310

Root Bridge with VLANs 313

Displaying Spanning-tree Status 318

IMPORTANT

STP is available only when the access point is in bridge mode.