Configuring Port Priority - Cisco Catalyst 3750 Software Configuration Manual

Chapter 14 Configuring STP

Configuring Port Priority

If a loop occurs, spanning tree uses the port priority when selecting an interface to put into the
forwarding state. You can assign higher priority values (lower numerical values) to interfaces that you
want selected first and lower priority values (higher numerical values) that you want selected last. If all
interfaces have the same priority value, spanning tree puts the interface with the lowest interface number
in the forwarding state and blocks the other interfaces.
Beginning in privileged EXEC mode, follow these steps to configure the port priority of an interface.
This procedure is optional.
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 spanning-tree port-priority priority
Step 4 spanning-tree vlan vlan-id port-priority priority
Step 5
end
Step 6
show spanning-tree interface interface-id
or
show spanning-tree vlan vlan-id
Step 7 copy running-config startup-config
Note The show spanning-tree interface interface-id privileged EXEC command displays information only
if the port is in a link-up operative state. Otherwise, you can use the show running-config interface
privileged EXEC command to confirm the configuration.
78-15870-01
Purpose
Enter global configuration mode.
Specify an interface to configure, and enter interface
configuration mode.
Valid interfaces include physical ports and port-channel
logical interfaces (port-channel port-channel-number).
Configure the port priority for an interface.
For priority, the range is 0 to 240, in increments of 16; the
default is 128. Valid values are 0, 16, 32, 48, 64, 80, 96,
112, 128, 144, 160, 176, 192, 208, 224, and 240. All other
values are rejected. The lower the number, the higher the
priority.
Configure the port priority for a VLAN.
For vlan-id, you can specify a single VLAN identified
•
by VLAN ID number, a range of VLANs separated by
a hyphen, or a series of VLANs separated by a comma.
The range is 1 to 4094.
• For priority, the range is 0 to 240, in increments of 16;
the default is 128. Valid values are 0, 16, 32, 48, 64, 80,
96, 112, 128, 144, 160, 176, 192, 208, 224, and 240.
All other values are rejected. The lower the number,
the higher the priority.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring Spanning-Tree Features
14-17