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Configuring Spanning-Tree Features
Configuring a Secondary Root Switch
When you configure a switch 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 VLAN 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 vlan vlan-id root primary global configuration command.
Beginning in privileged EXEC mode, follow these steps to configure a switch to become the secondary
root for the specified VLAN. This procedure is optional.
Command
Step 1
configure terminal
Step 2
spanning-tree vlan vlan-id root secondary
[diameter net-diameter [hello-time
seconds]]
Step 3
end
Step 4
show spanning-tree detail
Step 5
copy running-config startup-config
To return to the default setting, use the no spanning-tree vlan vlan-id root global configuration
command.
Configuring Port Priority
If a loop occurs, spanning tree uses the port priority when selecting an NNI to put into the forwarding
state. You can assign higher priority values (lower numerical values) to NNIs that you want selected first
and lower priority values (higher numerical values) to ones that you want selected last. If all NNIs have
the same priority value, spanning tree puts the NNI with the lowest interface number in the forwarding
state and blocks the other interfaces.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
14-16
Purpose
Enter global configuration mode.
Configure a switch to become the secondary 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.
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
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 14
Configuring STP
"Configuring the
14-14.
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Troubleshooting
