Technical data

ServerIron Switching and Routing Guide

Replace the <portnum> with a port that has redundant uplinks on a wiring closet switch.

Modifying Spanning Tree Parameters

Spanning Tree bridge and port parameters are configurable using the spanning-tree command. When no port-

based VLANs are active on the system, spanning tree parameters are set at the Global CONFIG Level.

When port-based VLANs are active on the system, spanning tree protocol bridge and port parameters can be

configured globally at the VLAN Level. Additionally, you can disable or enable STP on an interface basis.

NOTE: If VLANs are active on a switch or router, spanning-tree will not be seen as an option at the Global

CONFIG Level of the CLI but will be an option of the VLAN Level.

All bridge and port parameters have default values and do not need to be modified unless required to match

network needs. Additionally, all values will be globally applied to the switch or router. By default this feature is

enabled on switches and disabled on routers.

You can modify the following STP Parameters:

1. Modify bridge parameters—forward delay, maximum age, hello time and priority

2. Modify port parameters—priority and path cost

Suppose you want to enable spanning tree on a system in which no port-based VLANs are active and change the

hello-time from the default value of 2 to 8 seconds. Additionally, suppose you want to change the path and priority

costs for port 5 only. To do so, enter the following commands.

ServerIron(config)#span hello-time 8

ServerIron(config)#span ethernet 5 path-cost 15 priority 64

To disable spanning tree on physical port 4 of a system with no VLANs operating:

ServerIron(config)#interface ethernet 4

ServerIron(config-if-4)no spanning-tree

Syntax: [no] spanning-tree [ethernet <portnum> path-cost <value> priority <value>] forward-delay <value> hello-

time <value> maximum-age <time> priority <value>

Bridge Parameters:

• forward-delay: Possible values: 4 – 30 seconds. Default is 15 seconds.

• max-age: Possible values: 6 – 40 seconds. Default is 20 seconds.

• hello-time: Possible values: 1 – 10 seconds. Default is 2 seconds.

• priority: Possible values: 1 – 65,535. Default is 32,768. A higher numerical value means a lower priority; thus,

the highest priority is 0.

Port Parameters:

• path: Possible values: 1-65,535. Default: Auto

• The default value ‘Auto’ means that the port will adjust the default value automatically based on the port

speed. The default value is based on the following formula: Half-duplex ports: 1000/port speed; Full-duplex

ports: (1000/port speed)/2

• Priority: possible values are 0-255. Default is 128. A higher numerical value means a lower priority; thus, the

highest priority is 0.