N o t e

Multiple Instance Spanning-Tree Operation

Overview

Overview

The switches covered in this guide, use the IEEE 802.1s Multiple Spanning Tree Protocol (MSTP) standard.

MSTP Features

802.1s Spanning Tree Protocol

Default Setting

Page Ref

 

 

 

Viewing MSTP Status and Configuration

n/a

page 4-49

Configuring MSTP Operation Mode and

Disabled

page 4-21

Global Parameters

 

and

 

 

following

Configuring Basic Port Connectivity

admin-edge-port: No-disabled

page 4-26

Parameters

auto-edge-port: Yes-enabled

and

 

bpdu-filter: No-disabled

following

 

 

 

bpdu-protection: No-disabled

 

 

hello-time: 2

 

 

path-cost: auto

 

 

point-to-point MAC: Force-True

 

 

priority: 128 (multiplier: 8)

 

 

root-guard: No-disabled

 

 

tcn-guard: No-disabled

 

 

loop protection: Send disable

 

Configuring MSTP Instance Parameters

instance (MSTPI): none

page 4-35

 

priority: 32768 (multiplier: 8)

 

Configuring MSTP Instance Per-Port

path-cost: auto

page 4-37

Parameters

priority: 128 (multiplier: 8)

 

Enabling/Disabling MSTP Spanning Tree

Disabled

page 4-40

Operation

 

 

Enabling an Entire MST Region at Once

n/a

page 4-40

 

 

 

Without spanning tree, having more than one active path between a pair of nodes causes loops in the network, which can result in duplication of mes- sages, leading to a “broadcast storm” that can bring down the network.

MSTP cannot protect against loops when there is an unmanaged device on the network that drops spanning tree packets, or may fail to detect loops where this is an edge port configured with client authentication (802.1X, Web and MAC authentication). To protect against the formation of loops in these cases, you can use the loop protection feature (see “Loop Protection” on page 4-70).

4-3