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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter14 Configuring STP Configuring Spanning-Tree Features
Note If your network consists of switches that both do and do not support the extended sy stem ID, it is unlikely
that the switch with the extended system ID support will become the root switch. The extended system
ID increases the switch priority value every time the VLAN number is greater than the priority of the
connected switches running older software.
Note The root switch for each spanning-tree instance shou ld b e a ba ckbon e or dist ribution sw it ch. D o no t
configure an access switch as the spanning-tree primary root.
Use the diameter keyword to specify the Layer 2 network diameter (that is, the maximum number o f
switch hops between any two end stations in the Layer 2 network). When you s pecify t he n etwo rk
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 t hro ugh t he spanning-tree vlan vlan- id
hello-time, spanning-tree vlan vlan-id forward-t ime, and the spanning-tree vlan vlan-id max-age
global configuration commands.
Beginning in privileged EXEC mode, follow these steps to configure a switch to become the root for the
specified VLAN. This procedure is optional.
To return to the default setting, use the no spanning-tree vlan vlan-id root global configuration
command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree vlan vlan-id root primary
[diameter net-diameter [hello-time seconds]] Configure a switch to become the root for the specified VLAN.
•For vlan-id, you can specify a single VLAN identified by
VLAN ID number, a range of VLANs separated by a
hyphen, or a series of VLANs separated by a comma. The
range is 1 to 4094.
•(Optional) For diameter net-diameter, specify the
maximum number of switches between any two end
stations. The range is 2 to 7.
•(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; the default is 2.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree detail Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.