User's Manual

21-20
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 21 Configuring MSTP
Configuring MSTP Features
Beginning in privileged EXEC mode, follow these steps to configure a switch as the secondary root
switch. This procedure is optional.
To return the switch to its default setting, use the no spanni
ng-tree mst instance-id root global
configuration command.
Configuring Port Priority
If a loop occurs, the MSTP 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, the MSTP puts the interface with the lowest interface number in the forwarding
state and blocks the other interfaces.
Note If your Catalyst 3750-X switch is a member of a switch stack, you must use the spanning-tree mst
[instance-id] cost cost interface configuration command instead of the spanning-tree mst [instance-id]
port-priority priority interface configuration command to select a port to put in the forwarding state.
Assign lower cost values to ports that you want selected first and higher cost values to ports that you
want selected last. For more information, see the “Configuring Path Cost” section on page 21-21.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
spanning-tree mst instance-id root
secondary [diameter net-diameter
[hello-time seconds]]
Configure a switch as the secondary root switch.
• For instance-id, you can specify a single instance, a range of
instances separated by a hyphen, or a series of instances
separated by a comma. The range is 0 to 4094.
• (Optional) For diameter net-diameter, specify the maximum
number of switches between any two end stations. The range is 2
to 7
. This keyword is available only for MST instance 0.
• (Optional) For hello-time seconds, specify the interval in
seconds between the generation of configuration messages by
the root switch. The range is 1 to 10 seconds; the default
is 2 seconds.
Use the same network diameter and hello-time values that you used
w
hen configuring the primary root switch. See the “Configuring the
Root Switch” section on page 21-18.
Step 3
end Return to privileged EXEC mode.
Step 4
show spanning-tree mst instance-id Verify your entries.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.