3Com 4200G 12-Port Configuration Manual page 136

122 C 20: MSTP C
HAPTER
Bridge Priority
Configuration
MSTP Operation Mode
Configuration
ONFIGURATION
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.
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.
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
1 Configure the current switch as the root bridge of spanning tree instance 1 and a
secondary root bridge of spanning tree instance 2.
<S4200G> system-view
System View: return to User View with Ctrl+Z.
[4200G] stp instance 1 root primary
[4200G] stp instance 2 root secondary
Root bridges are selected by the bridge priorities of switches. You can make a specific
switch being selected as a root bridge by set a higher bridge priority for the switch
(Note that a smaller bridge priority value indicates a higher bridge priority.) A
MSTP-enabled switch can have different bridge priorities in different spanning tree
instances.
Configuration procedure
Table 88 Assign a bridge priority to a switch
Operation
Enter system view
Set a bridge priority for
a switch
CAUTION: 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 is not configurable.
During the selection of root bridge, if multiple switches have the same bridge priority,
the one with the least MAC address will become the root bridge.
Configuration example
1 Set the bridge priority of the current switch to 4,096 in spanning tree instance 1.
<S4200G> system-view
System View: return to User View with Ctrl+Z.
[4200G] stp instance 1 priority 4096
A MSTP-enabled switch can operate in one of the following operation modes:
STP mode: In this mode, the protocol packets sent out of the ports of the switch
■
are STP packets. If the switched network contains STP-enabled switches, you can
configure the current MSTP-enabled switch to operate in this mode by using the
stp mode stp command.
Command
system-view
stp [ instance instance-id ]
priority priority
Description
—
Required
The default bridge priority of a
switch is 32,768.