3Com Switch 8800 Family Configuration Guide

136 CHAPTER 17: MSTP REGION-CONFIGURATION
the switch ports send MSTP or STP packets (when 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 a STP switch in the switching network, you
may 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.
Generally, if there is a 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 transit back to MSTP mode after the STP switch is
removed. In this case, you can execute the stp mcheck command to restore the
MSTP mode.
By default, the switch runs in MSTP mode.
Configuring the Bridge
Priority for a Switch
Whether a switch can be elected as the spanning tree root depends on its Bridge
priority. The switch configured with a smaller Bridge priority is more likely to
become the root. An MSTP switch may have different priorities in different STIs.
You can use the following command to configure the Bridge priorities of the
Designated bridge in different STIs.
Perform the following configuration in system view.
When configuring the switch priority with the instance instance-id parameter as
0, you are configuring the CIST priority of the switch.
c
CAUTION: In the process of spanning tree root election, of two or more switches
with the same Bridge priorities, the one has a smaller MAC address is elected as
the root.
By default, the switch Bridge priority is 32768.
Configuring the Max
Hops in an MST Region
The scale of MST region is limited by the max hops in an MST region, which is
configured on the region root. As the BPDU travels from the spanning tree root,
Tabl e 109 Configure the MSTP running mode
Operation Command
Configure MSTP to run in STP-compatible mode stp mode stp
Configure MSTP to run in MSTP mode stp mode mstp
Restore the default MSTP running mode undo stp mode
Tabl e 110 Configure the Bridge priority for a switch
Operation Command
Configure the Bridge priority of the
Designated bridge
stp [ instance instance-id ] priority priority
Restore the default Bridge priority of the
Designated bridge
undo stp [ instance instance-id ] priority