3Com 4210 PWR, Configuration Manual

Page: 159 / 567

Configuring Root Bridge 157
When the root bridge fails or is turned off, the secondary root bridge becomes the
root bridge if no new root bridge is configured. If you configure multiple
secondary root bridges for a spanning tree instance, the one with the smallest
MAC address replaces the root bridge when the latter fails.
You can specify the network diameter and the hello time parameters while
configuring a root bridge/secondary root bridge. Refer to “Configuring the
Network Diameter of the Switched Network” on page 161 and “Configuring the
Timeout Time Factor” on page 162 for information about the network diameter
parameter and the hello time parameter.
n
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You can configure a switch as the root bridges of multiple spanning tree
instances. But you cannot configure two or more root bridges for one spanning
tree instance. So, do not configure root bridges for the same spanning tree
instance on two or more switches using the
stp root primary command.
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You can configure multiple secondary root bridges for one spanning tree
instance. That is, you can configure secondary root bridges for the same
spanning tree instance on two or more switches using the
stp root secondary
command.
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You can also configure the current switch as the root bridge by setting the
priority of the switch to 0. Note that once a switch is configured as the root
bridge or a secondary root bridge, its priority cannot be modified.
Configuration example
# Configure the current switch as the root bridge of spanning tree instance 1 and
a secondary root bridge of spanning tree instance 2.
<4210> system-view
[4210] stp instance 1 root primary
[4210] stp instance 2 root secondary
Configuring the Bridge
Priority of the Current
Switch
Root bridges are selected according to the bridge priorities of switches. You can
make a specific switch be selected as a root bridge by setting a lower bridge
priority for the switch. An MSTP-enabled switch can have different bridge priorities
in different spanning tree instances.
Configuration procedure
c
CAUTION:
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Once you specify a switch as the root bridge or a secondary root bridge by
using the
stp root primary or stp root secondary command, the bridge
priority of the switch cannot be configured any more.
Table 105 Configure the bridge priority of the current switch
Operation Command Description
Enter system view system-view -
Set the bridge priority for the
current switch stp [ instance instance-id ]
priority priority
Required
The default bridge priority of
a switch is 32,768.