Which of the following is NOT a field in the STP Bridge ID?

The Bridge ID in Spanning Tree Protocol (STP) is key in determining the role of a switch in a network topology. The Bridge ID is comprised of three main components that work together to uniquely identify a Bridge within a network.

The correct answer, which is Port ID, is not a part of the Bridge ID. The Bridge ID consists of the Bridge Priority, which allows network administrators to influence the design of the network by determining which bridge will become the root bridge, and the Extended System ID, which includes the VLAN ID, making it context-specific for VLAN configurations. Additionally, the MAC Address of the switch is included as part of the Bridge ID, providing a unique identifier for the switch hardware.

In contrast, the Port ID is an identifier for an individual port on a switch and is used in the context of defining path costs and roles on a switch-per-port basis. Therefore, while the Port ID is essential in the STP process, it is not part of the Bridge ID itself. Understanding these distinctions is crucial for effectively working with STP in network design and management.