Users Guide

Modifying Interface Parameters
On interfaces in Layer 2 mode, you can set the port cost and port priority values.
• Port cost — a value that is based on the interface type. The previous table lists the default values. The greater the port cost,
the less likely the port is selected to be a forwarding port.
• Port priority — influences the likelihood that a port is selected to be a forwarding port in case that several ports have the
same port cost.
To change the port cost or priority of an interface, use the following commands.
• Change the port cost of an interface.
INTERFACE mode
spanning-tree rstp cost cost
The range is from 0 to 65535.
The default is listed in the previous table.
• Change the port priority of an interface.
INTERFACE mode
spanning-tree rstp priority priority-value
The range is from 0 to 15.
The default is 128.
To view the current values for interface parameters, use the show spanning-tree rstp command from EXEC privilege
mode.
Influencing RSTP Root Selection
RSTP determines the root bridge, but you can assign one bridge a lower priority to increase the likelihood that it is selected as
the root bridge.
To change the bridge priority, use the following command.
• Assign a number as the bridge priority or designate it as the primary or secondary root.
PROTOCOL SPANNING TREE RSTP mode
bridge-priority priority-value
– priority-value The range is from 0 to 65535. The lower the number assigned, the more likely this bridge becomes
the root bridge.
The default is 32768. Entries must be multiples of 4096.
Example of the bridge-priority Command
A console message appears when a new root bridge has been assigned. The following example example shows the console
message after the bridge-priority command is used to make R2 the root bridge (shown in bold).
Dell(conf-rstp)#bridge-priority 4096
04:27:59: %SYSTEM-P:RP2 %SPANMGR-5-STP_ROOT_CHANGE: RSTP root changed. My Bridge ID:
4096:0001.e80b.88bd Old Root: 32768:0001.e801.cbb4 New Root: 4096:0001.e80b.88bd
Configuring an EdgePort
The EdgePort feature enables interfaces to begin forwarding traffic approximately 30 seconds sooner.
In this mode an interface forwards frames by default until it receives a BPDU that indicates that it should behave otherwise; it
does not go through the Learning and Listening states. The
bpduguard shutdown-on-violation option causes the
Rapid Spanning Tree Protocol (RSTP) 810