ue identifier and a configurable priority number; the bridge ID contains both numbers. To compare two bridge IDs, the priority is compared first. If two bridges have equal priority, then the media access control (MAC) addresses are compared. For example, if switches A (MAC=0200.0000.1134) = and B (MAC = 0200.0000.2452) both have a priority of 10, then switch A will be selected as the root bridge. If the network administrators would like switch B to become the root bridge, they must set its priority to be less than 10. In the network of Figure B.1, the smallest bridge ID is 2. Therefore, bridge 2 is the root bridge. Step 2: Determine the Least-Cost Paths to the Root Bridge The computed spanning tree has the property that messages from any connected device to the root bridge traverse a least-cost path. It is a path from the device to the root that has minimum cost among all paths from the device to the root. The cost of traversing a path is the sum of the costs of the segments on the path. Different technologies have different default costs for network segments. An administrator can con- figure the cost of traversing a particular network segment. The property that messages always traverse least-cost paths to the root is guaranteed by the following rules: Least-cost path from each bridge: After the root bridge has been chosen, each bridge determines the cost of each possible path from itself to the root. From these, it picks one with the smallest cost. The port connecting to that path becomes the root port (RP) of the bridge. Least-cost path from each network segment: The bridges on a network segment collec- tively determine which bridge has the least-cost path from the network segment Appendix B: Spanning Tree Protocol Bridge 1 root bridge Bridge 4 Link 8 Spanning tree Link 1 Link 2 Link 4 Link 5 Link 7 Bridge 2 Bridge 5 Bridge 6 Bridge 3 Link 3 Link 6 FIGURE B.2 Example of spanning tree computation via the assignment of port roles. to the root. The port connecting this bridge to the network segment is then the des