Installation and Getting Started Guide

STP Parameters and Defaults

Table 5.1 lists the default STP bridge parameters. The bridge parameters affect the entire VLAN (or the entire device, if the only port-based VLAN is the default one, VLAN 1).

Table 5.1: Default STP Bridge Parameters

Parameter

Description

Default and Valid Values

 

 

 

Forward Delay

The period of time a bridge will wait (the listen and learn

15 seconds

 

period) before beginning to forward data packets.

Possible values: 4 – 30

 

 

 

 

seconds

 

 

 

Maximum Age

The interval a bridge will wait for a hello packet from the

20 seconds

 

root bridge before initiating a topology change.

Possible values: 6 – 40

 

 

 

 

seconds

 

 

 

Hello Time

The interval of time between each configuration BPDU

2 seconds

 

sent by the root bridge.

Possible values: 1 – 10

 

 

 

 

seconds

 

 

 

Priority

A parameter used to identify the root bridge in a

32768

 

spanning tree (instance of STP). The bridge with the

Possible values: 0 – 65535

 

lowest value has the highest priority and is the root.

 

 

 

A higher numerical value means a lower priority; thus,

 

 

the highest priority is 0.

 

 

 

 

Table 5.2 lists the default STP port parameters. The port parameters affect individual ports and are separately configurable on each port.

Table 5.2: Default STP Port Parameters

Parameter

Description

Default and Valid Values

 

 

 

Priority

The preference that STP gives this port relative to other

128

 

ports for forwarding traffic out of the spanning tree.

Possible values: 0 – 255

 

 

 

A higher numerical value means a lower priority; thus,

 

 

the highest priority is 0.

 

 

 

 

Path Cost

The cost of using the port to reach the root bridge. When

10 Mbps – 100

 

selecting among multiple links to the root bridge, STP

100 Mbps – 19

 

chooses the link with the lowest path cost and blocks the

 

 

 

other paths. Each port type has its own default STP path

Gigabit – 4

 

cost.

Possible values are 0 –

 

 

 

 

65535

 

 

 

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