Introduction to the industrial Ethernet redundancy principle of industrial switches:

1. In a bridged LAN, in order to enhance reliability, a redundant path must be established, and the network segments will be connected by redundant bridges.

However, in a transparent bridge network, redundant paths can establish a bridge circuit, which is fatal to a local area network. It will bring the following problems:

A. Broadcast storm B. Multiple copies of the same frame C. Unstable MAC address table

Therefore, there must be a mechanism in the switched network to prevent loops.

2. Spanning tree protocol Spanning tree protocol is a commonly used mechanism in the IT industry. Spanning tree protocol is a bridge nesting protocol, defined in the IEEE 802.1d specification, which can be used to eliminate bridge loops. Its working principle is as follows: the spanning tree protocol defines a data packet called bridge protocol data unit BPDU (Bridge Protocol Data Unit). The bridges use BPDUs to communicate with each other, and use the related functions of BPDUs to dynamically select the root bridge and backup bridge. But since only one path exists from the central bridge to any network segment, bridge loops are eliminated.

In a spanning tree environment, bridges do not start forwarding immediately, they must first elect a bridge as the root bridge, and then establish a designated path. The bridge with the lowest bridge ID in a network will become a root bridge, and there is only one root bridge in all spanning tree networks. The main responsibility of the root bridge is to send configuration information periodically, and then this configuration information will be sent by all designated bridges. This is a mechanism in the spanning tree network. Once the network structure changes, the network state will be reconfigured.

After selecting the root bridge, before forwarding data packets, they must determine the designated bridge for each network segment. Using this algorithm of spanning tree, the root bridge sends BPDU packets from all its ports every 2 seconds. BPDU packets Copied by all bridges from their root ports, which are those bridge ports connected to the root bridge.

The information included in the BPDU is called the port's COST. The network administrator assigns the port's COST to all bridge ports. When the root bridge sends a BPDU, the root bridge sets its port value to zero. Then along the path, the next bridge increments its configured port COST to the value it receives and forwards packets to on the next segment.

In this way each bridge increases its port COST value to the COST value of the BPDU packet it receives, all bridges check their port COST values, and the bridge with the lowest port COST value becomes the designated bridge . A bridge with a relatively high port COST value puts its ports into a blocking state and becomes a backup bridge. In the blocking state, a bridge stops forwarding, but it continues to receive and process BPDU packets.

The IEEE 802.1D specification includes the Spanning Tree Algorithm (STA), a mechanism to ensure that forwarding loops never occur.

STA uses Bridge Protocol Data Units (Bridge Protocol Data Units, BPDU) to automatically configure independent ports on the bridge that are in the forwarding or blocking state. BPDUs are messages sent by bridges to a saved multicast MAC address (01-80-C2-00-00-00 for Ethernet) on which all transparent bridges listen. In the blocking state, the port does not learn or forward received frames. The end result of STA is a loop-free bridging environment that always exists regardless of changes in the topology of the LAN segment. The spanning tree algorithm determines the network link failure recovery time, which is at least 15 seconds.

Spanning tree state: A port on a switch running the spanning tree protocol is always in one of the following five states:

Blocking: All ports start in the blocking state to prevent loops, and the spanning tree determines which port switches to the forwarding state, and the port in the blocking state does not forward data frames but accepts BPDUs.

Listening: Data frames are not forwarded, but BPDUs (temporary state) are detected.

Learning: Do not forward data frames, but learn MAC address table (temporary state).

Forwarding: Data frames can be transmitted and received.

Disabled: Usually caused by a port failure or a misconfigured switch.

3. Conclusion The industrial network environment needs a rapid response redundancy mechanism, and the 15-second recovery time of the spanning tree protocol cannot meet the requirements of the industrial environment. Only the Supreme-Ring protocol is the best redundancy mechanism for industrial network environment.