20-19
Specify the current switch as the secondary root bridge of a spanning tree
Follow these steps to specify the current switch as the secondary root bridge of a spanning tree:
To do...
Use the command...
Remarks
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
Using the
stp
root primary
/
stp root secondary
command, you can specify the current switch as the
root bridge or the secondary root bridge of the MSTI 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 MSTIs. That is, it can be the root bridges in an MSTI and be
a secondary root bridge in another MSTI at the same time. But in the same MSTI, 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 an MSTI, 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
and
Configuring the MSTP Time-related Parameters
for information about the network diameter parameter
and the hello time parameter.
z
You can configure a switch as the root bridges of multiple MSTIs. But you cannot configure two or
more root bridges for one MSTI. So, do not configure root bridges for the same MSTI on two or
more switches using the
stp root primary
command.
z
You can configure multiple secondary root bridges for one MSTI. That is, you can configure
secondary root bridges for the same MSTI on two or more switches using the
stp root secondary
command.
z
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 MSTI 1 and a secondary root bridge of MSTI 2.
<Sysname> system-view
[Sysname] stp instance 1 root primary
[Sysname] stp instance 2 root secondary
