If the RSTP port cost is 20,000, what is the corresponding link speed?

In Rapid Spanning Tree Protocol (RSTP), the port cost is determined based on the speed of the link. Cisco uses a specific formula to calculate the port cost, which is derived from the bandwidth of the link. The costs associated with different link speeds are standardized.

When considering a port cost of 20,000, it corresponds to a link speed of 1 Gbps (Gigabit per second). This is based on the port cost values defined by IEEE 802.1D (which is the standard for Spanning Tree Protocol) and commonly adopted in networking practices.

In this case, 1 Gbps has a defined port cost of 20,000. The higher speeds have lower port costs because they can transmit more data per second, which is why as the speeds increase, the costs decrease in accordance with the standard.

Hence, knowing the RSTP port cost value allows you to infer the link speed accurately, confirming that a port cost of 20,000 is indeed indicative of a 1 Gbps link speed.