For a 100 Mbps interface in an 802.1D STP network, what is the cost assigned to it?

In an 802.1D Spanning Tree Protocol (STP) network, the cost of a network connection is determined based on the speed of the interface. The cost is a value that reflects the bandwidth of the link—lower costs are assigned to faster links, promoting their preferred use in the STP topology.

For a 100 Mbps interface, a cost of 19 is assigned based on the standard STP cost value for this bandwidth. This means that when the STP algorithm calculates the best path to the root bridge, it will favor the path with the lowest cost. Therefore, a 100 Mbps link, assigned a cost of 19, is treated as a more efficient route compared to slower links with higher cost values.

This assignment is based on the original IEEE 802.1D standard, which provides a defined set of cost values for various speeds, ensuring consistency and effectiveness in the STP process.