118 RackSwitch G8000: Application Guide
Port Priority
The port priority helps determine which bridge port becomes the root port or the
designated port. The case for the root port is when two switches are connected
using a minimum of two links with the same path-cost. The case for the designated
port is in a network topology that has multiple bridge ports with the same path-cost
connected to a single segment, the port with the lowest port priority becomes the
designated port for the segment. Use the following command to configure the port
priority:
where priority value is a number from 0 to 255, in increments of 16 (such as 0, 16,
32, and so on). If the specified priority value is not evenly divisible by 16, the value
will be automatically rounded down to the nearest valid increment whenever
manually changed in the configuration, or whenever a configuration file from a
release prior to N/OS 6.5 is loaded.
Port Path Cost
The port path cost assigns lower values to high-bandwidth ports, such as 10 Gigabit
Ethernet, to encourage their use. The objective is to use the fastest links so that the
route with the lowest cost is chosen. A value of 0 (the default) indicates that the
default cost will be computed for an auto-negotiated link or trunk speed.
Use the following command to modify the port path cost:
The port path cost can be a value from 1 to 200000000. Specify 0 for automatic path
cost.
RS G8000(config)# spanning-tree stp <STG> priority <priority value>
RS G8000(config)# interface port <port number>
RS G8000(config-if)# spanning-tree stp <STG> path-cost <path cost value>
RS G8000(config-if)# exit
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