3Com MSR 50 Series, Configuration Manual

Page: 463 / 2443

Configuring the Root Bridge 463
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CAUTION:
■
Upon specifying the current device as the root bridge or a secondary root
bridge, you cannot change 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 MST
region, its hop count is decremented 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.
When a device becomes the root bridge of the CIST or MSTI of an MST region, the
maximum hop in the configuration BPDUs generated by this device defines the
network diameter of the spanning tree to define how far the spanning tree can
reach in this MST region. All the devices other than the root bridge in the MST
region use the maximum hop value set for the root bridge.
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.
Configuration example
# Set the maximum hops of the MST region to 30.
<Sysname> system-view
[Sysname] stp max-hops 30
Configure the priority of the
current device stp [ instance instance-id ]
priority priority
Optional
32768 by default
To do... Use the command... Remarks
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