3Com 10014298 manual Configure the Port Priority, Instance instance-id port, Priority priority

200CHAPTER 8: STP OPERATION

In calculating the path cost of aggregation links, the 802.1D-1998 does not take into account the number of aggregation links, but the 802.1T does. The formula involved is:

Path Cost = 200,000,000/link speed in 100Kbps

Where the link speed is the sum of the speed of the ports in unblocked status within the aggregation links.

Configuring the Priority For spanning tree calculation, the port priority is an important factor when

of a Port determining if a port can be elected as the root port. With other attributes being equal, the port with the highest priority is elected as the root port. On the MSTP switch, a port can have different priorities in different STIs, and play different roles. The traffic from different VLANs can run over different physical links, thereby implementing the VLAN-based load-balancing.

You can configure the port priority in the following ways.

Configuring in System View

Perform the following configuration in system view.

Table 206 Configure the Port Priority

Operation	Command
Configure the port priority.	stp interface interface-list
	instance instance-idport
	priority priority

Restore the default port priority.

undo stp interface interface-listinstance instance-idport priority

Configuring in Ethernet Port View

Perform the following configuration in Ethernet port view.

Table 207 Configure the Port Priority

Operation	Command
Configure the port priority.	stp instance instance-idport
	priority priority
Restore the default port priority.	undo stp instance instance-id
	port priority

For more about the commands, see the Switch 7750 Command Reference Guide.

After the change of port priority, MSTP will recalculate the port role and transit the state. A smaller value represents a higher priority. If all the Ethernet ports of a switch are configured with the same priority value, the priorities of the ports will be differentiated by the index number. The change of Ethernet port priority will lead to spanning tree recalculation. You can configure the port priority with actual networking requirements.

By default, the priority of all the Ethernet ports is 128.