3Com 4500G Series, Руководство по настройке, Страница: 96 / 1206

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After configuring a 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.
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
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 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 can no longer take part in
spanning tree calculation, and thereby the size of the MST region is confined.
Make this configuration on the root bridge only. All the devices other than the root bridge in the MST
region use the maximum hop value set for the root bridge.
Follow these steps to configure the maximum number of hops of an 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
Required
20 by default
Configuring the Network Diameter of a Switched Network
Any two terminal devices in a switched network are interconnected through a specific path composed of
a series of devices. The network diameter is the number of devices on the path composed of the most
devices. The network diameter is a parameter that indicates the network size. A bigger network
diameter indicates a larger network size.
Make this configuration on the root bridge only.
Follow these steps to configure the network diameter of a switched network:
To do... Use the command... Remarks
Enter system view
system-view
—
Configure the network diameter
of the switched network
stp bridge-diameter diameter
Required
7 by default