3Com Switch 7750 Configuration Guide

262 CHAPTER 30: MSTP CONFIGURATION
Changing the path cost of a port may change the role of the port and put it in
state transition. Executing the stp cost command with the instance-id argument
being 0 sets the path cost on the CIST for the port.
Configuration example (A)
# Configure the path cost of Ethernet1/0/1 port in spanning tree instance 1 to be
2,000.
1 Configure in system view.
<SW7750> system-view
[SW7750] stp interface ethernet1/0/1 instance 1 cost 2000
2 Configure in Ethernet port view.
<SW7750> system-view
[SW7750] interface ethernet1/0/1
[SW7750-Ethernet1/0/1] stp instance 1 cost 2000
Configuration example (B)
# Change the path cost of Ethernet1/0/1 port in spanning tree instance 1 to the
default one calculated with the IEEE 802.1D-1998 standard.
<SW7750> system-view
[SW7750] stp pathcost-standard dot1d-1998
Port Priority
Configuration
Port priority is an important criterion on determining the root port. In the same
condition, ports with smaller port priority values are more potential to become the
root port than those with bigger priority values.
A port on a MSTP-enabled switch can have different port priorities and play
different roles in different spanning tree instances. This enables packets of
different VLANs to be forwarded along different physical paths, so that load
balancing can be achieved by VLANs.
You can configure port priority in the following two ways.
Configuring port priority in system view
Configure the path
cost for the port
stp [ instance instance-id ] cost
cost
Required
A MSTP-enabled switch can
calculate path costs for all its ports
automatically.
Table 193 Configure the path cost for a port in Ethernet port view
Operation Command Description
Table 194 Configure port priority for specified ports in system view
Operation Command Description
Enter system view system-view -
Configure port priority
for specified ports
stp interface interface-list
instance instance-id port
priority priority
Required
The default port priority is 128.