19-19
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
OL-12247-04
Chapter 19 Configuring MSTP
Configuring MSTP Features
Configuring a Secondary Root Switch
When you configure a switch with the extended system ID support as the secondary root, the switch
priority is modified from the default value (32768) to 28672. The switch is then likely to become the root
switch for the specified instance if the primary root switch fails. This is assuming that the other network
switches use the default switch priority of 32768 and therefore are unlikely to become the root switch.
You can execute this command on more than one switch to configure multiple backup root switches. Use
the same network diameter and hello-time values that you used when you configured the primary root
switch with the
spanning-tree mst
instance-id
root primary
global configuration command.
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 spanning-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.
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
when configuring the primary root switch. See the
Root Switch” section on page 19-17
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.