3Com Switch 7750 Configuration Guide

250 CHAPTER 30: MSTP CONFIGURATION
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
# Configure the current switch as the root bridge of spanning tree instance 1 and
a secondary root bridge of spanning tree instance 2.
<SW7750> system-view
[SW7750] stp instance 1 root primary
[SW7750] stp instance 2 root secondary
Bridge Priority
Configuration
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
c
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 the root bridge, if multiple switches have the same
bridge priority, the one with the least MAC address becomes the root bridge
candidate.
Configuration example
# Set the bridge priority of the current switch to 4,096 in spanning tree instance 1.
<SW7750> system-view
[SW7750] stp instance 1 priority 4096
MSTP Operation Mode
Configuration
A MSTP-enabled switch can operate in one of the following operation modes:
■ STP-compatible 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.
■ RSTP-compatible mode: In this mode, the protocol packets sent out of the
ports of the switch are RSTP packets. If the switched network contains
Table 175 Assign a bridge priority to a switch
Operation Command Description
Enter system view system-view -
Set a bridge priority
for the current switch
stp [ instance instance-id ]
priority priority
Required
The default bridge priority of a
switch is 32,768.