What are Port Cost, Port Priority and Path Cost Values
To find the Root Port, the Port Cost of ports are calculated. The cost of a port is inversely related to the associated bandwidth and therefore a port with a low cost value is more preferable than a port with high cost value. Another value associated with ports is known as Port Priority Value, which is equal to 32 by default. A lower port priority value is preferred, as in the case Switch priority value. The following table lists the Port Cost value for different bandwidths.
Link Speed
Cost Value
10 Gbps
2
1 Gbps
4
100 Mbps
19
10 Mbps
100
A Path Cost can be defined as the accumulated port costs from a switch to the root switch. When a switch receives a Bridge Protocol Data Unit (BPDU) in its port, it increments the path cost with the cost of the incoming port. Path costs are incremented when a Bridge Protocol Data Unit (BPDU) reaches a port.
