Allied Telesis 2.6.1 manual SET STP=stpnameALL PRIORITY=0..65535

Layer 2 Switching 89

by the Root Bridge. The FORWARDDELAY, MAXAGE and HELLOTIME parameters are interrelated. See the note and formulae below. The default value for FORWARDDELAY is 15 seconds.

The HELLOTIME parameter sets the time, in seconds, between the transmission of switch spanning tree configuration information when the switch is the Root Bridge of the spanning tree or is trying to become the Root Bridge. The default value is 2 seconds.

The MAXAGE parameter sets the maximum age, in seconds, of Spanning Tree Protocol information learned over the network on any port before it is discarded. The default value is 20 seconds.

The FORWARDDELAY, MAXAGE and HELLOTIME parameters should be set according to the following formulae, as specified in IEEE Standard 802.1D:

2 x (FORWARDDELAY - 1.0 seconds) >= MAXAGE MAXAGE >= 2 x (HELLOTIME + 1.0 seconds)

To modify the parameters controlling these time intervals, use the command:

SET STP={stp-nameALL} [FORWARDDELAY=4..30] [HELLOTIME=1..10] [MAXAGE=6..40] [other parameters]

The value of the PRIORITY parameter is used to set the writable portion of the bridge ID, i.e. the first two octets of the (8-octet long) Bridge Identifier. The remaining 6 octets of the bridge ID are given by the MAC address of the switches. The Bridge Identifier parameter is used in all configuration Spanning Tree Protocol packets transmitted by the switch. The first two octets, specified by the PRIORITY parameter, determine the switch’s priority for becoming the root bridge or a designated bridge in the network, with a lower number indicating a higher priority. In fairly simple networks, for instance those with a small number of switches in a meshed topology, it may make little difference which switch is selected to be the root bridge, and no modifications may be needed to the default PRIORITY parameter, which has a default value of 32768. In more complex networks, one or more switches are likely to be more suitable candidates for the root bridge role, for instance by virtue of being more central in the physical topology of the network. In these cases the STP PRIORITY parameters for at least one of the switches should be modified.

To change the STP priority value, use the command:

SET STP={stpnameALL} PRIORITY=0..65535

The PRIORITY parameter sets the priority of the switch to become the Root Bridge. The lower the value of the Bridge Identifier, the higher the priority. If the PRIORITY parameter is set, either by specifying the PRIORTY or DEFAULT parameters, the specified STP is initialised. Counters for the STP are not affected. The default value for PRIORITY is 32768.

To restore STP timer and priority defaults, use the command:

SET STP={stpnameALL} DEFAULT

Changing the STP PRIORITY using either of the previous commands initialises the STP, so that elections for the root bridge and designated bridges begin again, without resetting STP counters. To display general information about STPs on the switch, use the command:

SHOW STP[={stpnameALL}] [SUMMARY]

Software Release 2.6.1 C613-02039-00 REV A