Command Reference Guide

SROS Command Line Interface Reference Guide ATM Sub-Interface Config Command Set

spanning-tree path-cost <value>

Use the bridge-group path-cost command to assign a cost to a bridge group that is used when computing

the spanning-tree root path. To return to the default path-cost value, use the no form of this command.

Syntax Description

<value> Number assigned to the bridge interface to be used as the path cost in spanning

calculations (valid range: 0 to 65535)

Default Values

<value> 19

Command Modes

(config-interface)# Interface Configuration Mode

Valid interfaces include: ATM sub-interface, Ethernet, virtual PPP interfaces, and

virtual Frame Relay interfaces.

Functional Notes

The specified value is inversely proportional to the likelihood the bridge interface will be chosen as the root

path. Set the path-cost value lower to increase the chance the interface will be the root. To obtain the most

accurate spanning-tree calculations, develop a system for determining path costs for links and apply it to

all bridged interfaces.

Usage Examples

The following example assigns a path cost of 100 for bridge group 17 on an ATM sub-interface:

(config)#interface atm 1.1

(config-atm 1.1)#spanning-tree path-cost 100

Technology Review

Spanning-tree protocol provides a way to prevent loopback or parallel paths in bridged networks. Using the

priority values and path costs assigned to each bridging interface, the spanning-tree protocol determines

the root path and identifies whether to block or allow other paths.