29.1.1 Overview

The Ring Protocol is a Layer 2 network redundancy protocol that detects faults in networks in which switches are connected in rings, and performs high-speed path switching accordingly.

Spanning Tree Protocols can be used as a Layer 2 network redundancy protocol, but suffer from shortcomings such as slow convergence for switching when faults occur. The Ring Protocol can be used to ensure that the path switching for when faults occur is performed at high speed. By using ring topology, the need for transmission paths and interfaces is reduced when compared to a mesh topology.

The following figure provides an overview of a ring network based on the Ring Protocol.

Figure 29-1 Overview of Ring Protocol

Of the nodes constituting a ring, one is the master node and the others are transit nodes. The two ports connecting each node are called ring ports, and the ring ports of the master node include a primary port and a secondary port. The master node can divide a ring configuration by applying a logical block to the secondary port to prevent data frame loops. The master node regularly sends control frames (health check frames) to monitor the status within a ring, and determines whether a fault has occurred within the ring based on whether the sent health check frames have been received or not. Master nodes that detect a fault or fault restoration set or remove a logical block on the secondary port to perform path switching and restore communication.