3Com Switch 8800 Advanced Software V5 Configuration Guide

Configuring the Root Bridge 113
Configuring the Priority
of the Current Device
The priority of a device determines whether it can be elected as the root bridge of
a spanning tree. A lower value indicates a higher priority. By setting the priority of
a device to a low value, you can specify the device as the root bridge of spanning
tree. An MSTP-compliant device can have different priorities in different MST
instances.
Configuration procedure
Follow these steps to configure the priority of the current device:
c
CAUTION:
■ Upon specifying the current device as the root bridge or a secondary root
bridge, you cannot configure the priority of the device.
■ During root bridge selection, if all devices in a spanning tree have the same
priority, the one with the lowest MAC address will be selected as the root
bridge of the spanning tree.
Configuration example
# Set the device priority in MST instance 1 to 4096.
<Sysname> system-view
[Sysname] stp instance 1 priority 4096
Configuring the
Maximum Hops of an
MST Region
By setting the maximum hops of an MST region, you can restrict the region size.
The maximum hops setting configured on the regional root bridge will be used as
the maximum hops of the MST region.
After a configuration BPDU leaves the root bridge of the spanning tree in the
region, its hop count is decreased by 1 whenever it passes a device. When its hop
count reaches 0, it will be discarded by the device that has received it. As a result,
devices beyond the maximum hops are unable to take part in spanning tree
computing, and thereby the size of the MST region is restricted.
Configuration procedure
Follow these steps to configure the maximum hops of the MST region
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A larger maximum hops setting means a larger size of the MST region. Only the
maximum hops configured on the regional root bridge can restrict the size of the
MST region.
To do... Use the command... Remarks
Enter system view system-view -
Configure the priority of the
current device
stp [ instance instance-id ]
priority priority
Optional
32768 by default
To do... Use the command... Remarks
Enter system view system-view -
Configure the maximum hops
of the MST region
stp max-hops hops Optional
20 by default