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Layer 2 Switching 53
Rapier Switch Software Release 2.2.1
C613-02013-00 Rev A
Each port has a port priority, with a default value of 128, used to determine
which port should be the root port for the STP if two ports are connected in a
loop. The lower number indicates the higher priority.
SET STP PORT={port-list|ALL} PORTPRIORITY=0..255 [other-
parameters...]
The PORTPRIORITY parameter sets the value of the priority field contained in
the port identifier. The Spanning Tree Algorithm uses the port priority when
determining the root port for each switch. The port with the lowest value is
considered to have the highest priority. The default value is 128. Each STP has
its own independent PORTPRIORITY parameter for each member port.
Each port also has a path cost, which is used if the port is the root port for the
STP on the switch. The path cost is added to the root path cost field in
configuration messages received on the port to determine the total cost of the
path to the root bridge. The default PATHCOST values depend on the port
speed, according to the formula:
PATHCOST = 1000 / Port_Speed_in_MB_per_second
so that a port operating at 10Mbps has a default pathcost of 100, a port
operating at 100 Mbps has a default pathcost of 10, and a port operating at 1
Gbps has a default pathcost of 1. Setting the pathcost to a larger value on a
particular port is likely to reduce the traffic over the LAN connected to it. This
may be appropriate if the LAN has lower bandwidth, or if there are reasons for
limiting the traffic across it. To modify the STP port pathcost, use the
command:
SET STP PORT={port-list|ALL} PATHCOST=1..1000000
If the PATHCOST of a port has not been explicitly set by the user, or the default
values have been restored to the port, then the default PATHCOST for the port
will vary as the speed of the port varies.
The default value for PATHCOST is set according to the speed. For a port
operating at 100 Mbps, the default value is 19. For a port operating at 10 Mbps,
the default value is 100.
Forward Delay The time ports spend in the Listening state and Learning
state before moving to the Learning or Forwarding state
respectively. Also the value used for the ageing timer for the
dynamic entries in the Forwarding Database while received
Configuration Messages indicate a topology change.
Switch Max Age The value of the Max Age parameter when this switch is the
Root or is attempting to become the Root. This parameter
is set by the MAXAGE parameter in the SET STP command.
Switch Hello Time The value of the Hello Time parameter when this switch is
the Root or is attempting to become the Root. This
parameter is set by the HELLOTIME parameter in the SET
STP command.
Switch Forward Delay The value of the Forward Delay parameter when this switch
is the Root or is attempting to become the Root. This
parameter is set by the FORWARDDELAY parameter in the
SET STP command.
Hold Time The minimum time in seconds between the transmission of
configuration BPDUs through a given LAN Port. The value
of this fixed parameter is 1, as specified in IEEE Std 802.1D.
Table 10: Parameters in the output of the SHOW STP command
Parameter Meaning