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Scaling the Spanning Tree Protocol

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The following switch output is an example of using the

set spantree

root

command:

Todd5000> (enable) set spantree root 1-4 dia 2

VLANs 1-2 bridge priority set to 8192.

VLANs 1-2 bridge max aging time set to 10.

VLANs 1-2 bridge hello time set to 2.

VLANs 1-2 bridge forward delay set to 7.

Switch is now the root switch for active VLANs 1-4.

Todd5000> (enable)

The set spantree root command tells the switch to change the bridge

priority to 8192, which will automatically change the switch to the root
bridge. The 1-4 represents the VLANs for which the STP will change the
parameters, and the dia 2 is the network diameter. To figure the network
diameter, we just counted the number of switches from the root, including
the root bridge, which in our example equaled 2.

Notice the output after the command. The bridge priority was changed to

8192, max age time to 10, hello time is still 2 seconds, and the forward delay
was set to 7 seconds. If the network diameter is set, the STP will set the timers
to what it would consider efficient for that size network.

You can verify your STP configuration with the show spantree com-

mand. If you type the command show spantree with no parameters, it will
show you the spanning tree configuration for all VLANs. You can type show
spantree vlan

to see the parameters for just a particular VLAN. The fol-

lowing switch output shows the spanning tree information for VLAN 1:

Todd5000> (enable) sh spantree 1

VLAN 1

Spanning tree enabled

Spanning tree type ieee

Designated Root 00-e0-34-88-fc-00

Designated Root Priority 8192

Designated Root Cost 0

Designated Root Port 1/0

Root Max Age 10 sec Hello Time 2 sec Forward Delay 7 sec

Bridge ID MAC ADDR 00-e0-34-88-fc-00

Bridge ID Priority 8192

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