How does the RSTP port cost relate to link speed?

The relationship between RSTP (Rapid Spanning Tree Protocol) port cost and link speed is such that a lower port cost corresponds to a faster link speed. RSTP uses port cost to reflect the speed of the link, where the cost is inversely proportional to the data rate of the link.

For instance, standard Ethernet links have predefined costs based on their bandwidth: a 100 Mbps Ethernet (Fast Ethernet) has a higher cost than a 1 Gbps Ethernet (Gigabit Ethernet). This configuration allows RSTP to make effective decisions about which paths to use in the network topology. If a link is faster, it will have a lower cost, meaning that it will be preferred over slower links when establishing the shortest path through the network.

This mechanism is crucial for ensuring that traffic flows efficiently and avoiding network loops, which can degrade performance. Therefore, in the context of RSTP, recognizing that a lower port cost reflects a faster link speed is essential for understanding how the protocol optimizes network performance.