H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 178)

20-20
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Upon specifying the current device as the root bridge or a secondary root bridge, you cannot
change the priority of the device.
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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.
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.
The regional root bridge always sends a configuration BPDU with a hop count set to the maximum value.
When a switch receives this configuration BPDU, it decrements the hop count by 1 and uses the new
hop count as the remaining hop count in the BPDUs it propagates. When the hop count of a BPDU
reaches 0, it is discarded by the device that received it. Thus, devices beyond the reach of the
maximum hop are unable to take part in spanning tree calculation, and thereby the size of the MST
region is confined.
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:
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
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.
system-view
[Sysname] stp max-hops 30