Port (computer networking)

Abstract: An improvement to the spanning tree protocol provides for identifying a port on the bridge in the alternate port role which qualifies as a candidate root port. Upon an event causing a topology change resulting in a particular port changing from the candidate root port role to the root port role and the previous root port changing to the designated port role, the process allows the previous root port to have the forwarding state without requiring transition through the listening and forwarding states. Qualification as a suitable candidate root port according is based upon propagating a message from the root bridge, such as a bridge protocol data unit (“BPDU”) message, carrying the identifier of the port on the root bridge from which the message originates. Logic in the bridges is able to identify the branch of the tree from which the message originates, and to select the candidate root port in response to the branch information. Thus, the port on a different branch than the root is a suitable candidate root port. A port on the same branch as the root is suitable if it has recently received (such as within one Hello time in the standard Spanning Tree) updated configuration information from its upstream bridge (Designated Bridge on the port), such as by a configuration BPDU.