3Com 7700 Configuration Manual page 236

228 C 8: STP O
HAPTER PERATION
Configuring the Bridge
Priority for a Switch
Configuring the Max
Hops in an MST Region
connected to the STP switch) and the switch provides multiple spanning tree
function.
You can use the following command to configure MSTP running mode. MSTP can
intercommunicate with STP. If there is STP switch in the switching network, you
can use the command to configure the current MSTP to run in STP-compatible
mode, otherwise, configure it to run in MSTP mode.
Perform the following configuration in system view.
Table 22 Configure the MSTP Running Mode
Operation
Configure MSTP to run in STP-compatible
mode
Configure MSTP to run in MSTP mode.
Restore the default MSTP running mode
Generally, if there is STP switch on the switching network, the port connected to it
will automatically transit from MSTP mode to STP-compatible mode. But the port
cannot automatically transition back to MSTP mode after the STP switch is
removed.
By default, MSTP runs in MSTP mode.
Whether a switch can be elected as the spanning tree root depends on its bridge
priority. The switch configured with a lower bridge priority is more likely to
become the root. An MSTP switch can have different priorities in different STIs.
You can use the following command to configure the bridge priorities of the
designated switch in different STIs.
Perform the following configuration in system view.
Table 23 Configure the Bridge Priority for a Switch
Operation
Configure the Bridge priority of the
designated switch.
Restore the default Bridge priority of the
designated switch.
When configuring the switch priority with the instance instance-id parameter
with a value of 0, you are configuring the CIST priority of the switch.
Caution: In the process of spanning tree root election, of two or more switches
with the lowest bridge priorities, the one has a smaller MAC address will be
elected as the root.
By default, the switch bridge priority is 32768.
The scale of an MST region is limited by the max hops in an MST region, which is
configured on the region root. As the BPDU traveling from the spanning tree root,
each time when it is forwarded by a switch, the max hops is reduced by 1. The
Command
stp mode stp
stp mode mstp
undo stp mode
Command
stp instance instance-id bridge-priority
priority
undo stp instance instance-id
bridge-priority