3Com Switch 8800 Advanced Software V5 Configuration Guide

Configuring the Root Bridge 111
Specifying the current device as the root bridge of a specific spanning tree
Follow these steps to specify the current device as the root bridge of a specific
spanning tree:
Specifying the current device as a secondary root bridge of a specific
spanning tree
Follow these steps to specify the current device as a secondary root bridge of a
specific spanning tree:
Note that:
■ Upon specifying the current device as the root bridge or a secondary root
bridge, you cannot change the priority of the device.
■ You can configure the current device as the root bridge or a secondary root
bridge of an MST instance, which is specified by instance instance-id in the
command. If you set instance-id to 0, the current device will be the root bridge
or a secondary root bridge of the CIST.
■ The current device has independent roles in different instances. It can act as the
root bridge or a secondary root bridge of one instance while it can also act as
the root bridge or a secondary root bridge of another instance. However, the
same device cannot be the root bridge and a secondary root bridge in the same
instance at the same time.
■ There is one and only one root bridge in effect in a spanning tree instance. If
two or more devices have been designated to be root bridges of the same
spanning tree instance, MSTP will select the device with the lowest MAC
address as the root bridge.
■ You can specify multiple secondary root bridges for the same instance. Namely,
you can specify secondary root bridges for the same instance on two or more
than two device.
■ When the root bridge of an instance fails or is shut down, the secondary root
bridge (if you have specified one) can take over the role of the instance.
However, if you specify a new root bridge for the instance at this time, the
secondary root bridge will not become the root bridge. If you have specified
multiple secondary root bridges for an instance, when the root bridge fails,
MSTP will select the secondary root bridge with the lowest MAC address as the
new root bridge.
To do... Use the command... Remarks
Enter system view system-view -
Specify the current device as
the root bridge of a specific
spanning tree
stp [ instance instance-id ]
root primary [
bridge-diameter bridgenum
] [ hello-time centi-seconds ]
Required
The device does not function
as the root bridge by default
To do... Use the command... Remarks
Enter system view system-view -
Specify the current device as a
secondary root bridge of a
specific spanning tree
stp [ instance instance-id ]
root secondary [
bridge-diameter bridgenum
] [ hello-time centi-seconds ]
Required
By default, a device does not
function as a secondary root
bridge.