Which device will become the root in the Spanning Tree election process?

The Spanning Tree Protocol (STP) elects a root bridge for a Layer 2 network by comparing the Bridge IDs (BIDs) of all participating switches. The switch with the numerically lowest BID becomes the root bridge. The BID is an 8-byte value composed of a 2-byte Bridge Priority and the switch's 6-byte MAC address. The election process first compares the priority values; the lowest priority is preferred. If the priorities are identical, the switch with the lowest MAC address is chosen as the root bridge.

A. Root Guard is a security feature that prevents a designated port from becoming a root port, thereby protecting the established root bridge's position, not electing one.

B. IP addresses are Layer 3 constructs and play no role in the Layer 2 STP election process.

D. The device with the lowest bridge priority value is preferred in the election process, not the highest. A higher value makes a device less likely to become the root.

1. RUCKUS FastIron Layer 2 Switching Configuration Guide, 08.0.95, Chapter 12: Spanning Tree Protocol (STP), Page 299, Section: "Root bridge election".

The document states: "The device with the lowest bridge ID becomes the root bridge. The bridge ID is an 8-byte value that consists of the 2-byte bridge priority and the 6-byte MAC address of the device." This directly supports that the lowest Bridge ID wins the election.

2. IEEE Std 802.1D-2004, "IEEE Standard for Local and Metropolitan Area Networks—Media Access Control (MAC) Bridges", Clause 17.3, "Spanning tree algorithm".

This standard, which defines the original Spanning Tree Protocol, specifies that the root is the bridge with the unique, lowest Bridge Identifier. This is the foundational principle for the election process.