3Com Switch 4800G 24-Port Configuration Manual page 215

Specifying the Root
Bridge or a Secondary
Root Bridge
n
MSTP can determine the root bridge of a spanning tree through MSTP calculation.
Alternatively, you can specify the current device as the root bridge using the
commands provided by the system.
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:
To do...
Enter system view
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:
To do...
Enter system view
Specify the current device as a
secondary root bridge of a
specific spanning tree
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 devices.
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,
Configuring the Root Bridge
Use the command...
system-view
stp [ instance instance-id ]
root primary
Use the command...
system-view
stp [ instance instance-id ]
root secondary
215
Remarks
-
Required
By default, a device does not
function as the root bridge.
Remarks
-
Required
By default, a device does not
function as a secondary root
bridge.