3Com Switch 7754, Configuration Manual, Page: 249 / 940

Root Bridge Configuration 249
Root Bridge/Secondary
Root Bridge
Configuration
MSTP can automatically choose a switch as a root bridge. You can also manually
specify the current switch as a root bridge by using the corresponding commands.
Root bridge configuration
Secondary root bridge configuration
Using the stp root primary / stp root secondary command, you can specify a
switch as the root bridge or the secondary root bridge of the spanning tree
instance identified by the
instance-id argument. If the value of the instance-id
argument is set to 0, the stp root primary / stp root secondary command specify
the current switch as the root bridge or the secondary root bridge of the CIST.
A switch can play different roles in different spanning tree instances. That is, it can
be the root bridges in a spanning tree instance and be a secondary root bridge in
another spanning tree instance at the same time. But in one spanning tree
instance, a switch cannot be the root bridge and the secondary root bridge
simultaneously.
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 least 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 “Network Diameter
Configuration” on page 252 and “MSTP Time-related Configuration” on page
252 for information about the network diameter parameter and the Hello time
parameter.
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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
Table 173 Specify the current switch as the root bridge of a specified spanning tree
Operation Command Description
Enter system view system-view -
Specify the current
switch as the root bridge
of a specified spanning
tree stp [ instance instance-id ] root primary
[ bridge-diameter bridgenumber
[ hello-time centi-seconds ] ]
Required
Table 174 Specify the current switch as the secondary root bridge of a specified spanning
tree
Operation Command Description
Enter system view system-view -
Specify the current switch
as the secondary root
bridge of a specified
spanning tree stp [ instance instance-id ] root
secondary [ bridge-diameter
bridgenumber [ hello-time
centi-seconds ] ]
Required