Allied Telesis Rapier Switch - Manual (Page 56)

56 Rapier Switch Software Reference
Software Release 2.5.1
C613-02025-00 REV B
is only used when the switch is acting as the Root Bridge. Any switch not
acting as the Root Bridge uses a dynamic value for the FORWARDDELAY set
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-name|ALL} [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={stpname|ALL} 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={stpname|ALL} 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[={stpname|ALL}] [SUMMARY]