Cisco 2950G 24 - Catalyst Switch Software Configuration Manual page 305

Chapter 12 Configuring RSTP and MSTP
Note 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.
We recommend that you avoid manually configuring the hello time, forward-delay time, and
Note
maximum-age time by using the spanning-tree mst hello-time, spanning-tree mst forward-time, and
the spanning-tree mst max-age global configuration commands after configuring the switch as the root
switch.
Beginning in privileged EXEC mode, follow these steps to configure a switch as the root switch:
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.
78-14982-01
Purpose
Enter global configuration mode.
Configure a switch as the root switch.
For instance-id, the range is 0 to 15.
•
(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.
Catalyst 2950 Desktop Switch Software Configuration Guide
Configuring RSTP and MSTP Features
12-15