Cisco Certified Network Professional 2025 – 400 Free Practice Questions to Pass the Exam

The traditional Bridge ID in Spanning Tree Protocol (STP) is made up of two main components: the bridge priority and the MAC address of the switch. The bridge priority is a configurable value that helps determine which switch will become the root bridge in the STP topology during the election process. The MAC address is unique to each switch and ensures that each Bridge ID is distinct.

Together, the bridge priority and the MAC address form a 64-bit identifier where the bridge priority typically occupies the first 16 bits, and the MAC address occupies the remaining 48 bits. The combination of these two values is what uniquely identifies a switch in the STP process.

This structure is critical for STP's operation of preventing loops in the network by allowing switches to successfully identify each other and make decisions about which paths to block or forward. Understanding this format is essential for effective network design and troubleshooting within STP environments.