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Configuring MSTP Features
The root switch for each spanning-tree instance should be a backbone or distribution switch. Do not
configure an access switch as the spanning-tree primary root.
Use the diameter keyword, which is available only for MST instance 0, to specify the Layer 2 network
diameter (that is, the maximum number of switch hops between any two end stations in the Layer 2
network). When you specify the network diameter, the switch automatically sets an optimal hello time,
forward-delay time, and maximum-age time for a network of that diameter, which can significantly
reduce the convergence time. You can use the hello keyword to override the automatically calculated
hello time.
Note
After configuring the switch as the root switch, we recommend that you avoid manually configuring the
hello time, forward-delay time, and maximum-age time through the spanning-tree mst hello-time,
spanning-tree mst forward-time, and the spanning-tree mst max-age global configuration
commands.
Beginning in privileged EXEC mode, follow these steps to configure a switch as the root switch. This
procedure is optional.
Command
Step 1
configure terminal
Step 2
spanning-tree mst instance-id root primary
[diameter net-diameter [hello-time seconds]]
Step 3
end
Step 4
show spanning-tree mst instance-id
Step 5
copy running-config startup-config
To return the switch to its default setting, use the no spanning-tree mst instance-id root global
configuration command.
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.
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
17-18
Purpose
Enter global configuration mode.
Configure a switch as the 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.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 17
Configuring MSTP
OL-8915-03
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