1 Introduction
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 network bridged by a transparent bridge, a redundant path can establish a bridge loop, 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 switching network to prevent loops.
2. Spanning Tree Protocol
Spanning tree protocol is a mechanism commonly used in the IT world. Spanning tree protocol is a bridge nesting protocol, defined in the IEEE 802.1d specification, can be used to eliminate bridge loops. Its working principle is this: Spanning Tree Protocol defines a data packet, called Bridge Protocol Data Unit (BPDU). Bridges use BPDUs to communicate with each other, and use the related functions of BPDUs to dynamically select the root and backup bridges. But because there is only one path from the central bridge to any network segment, the bridge loop is eliminated.
In a spanning tree environment, bridges will not immediately start the forwarding function, they must first select a bridge as the root bridge, and then establish a designated path. The one 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 periodically send configuration information, 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.
When the root bridge is selected, before forwarding packets, they must decide on 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 All bridges are copied from their root ports. The root ports are those bridge ports connected to the root bridge. The information included in the BPDU is called the port COST. The network administrator assigns the port COST to all bridge ports. When the root bridge sends a BPDU, the root bridge sets its port value to zero. Then along this path, the next bridge increases its configuration port COST to a value, which is the value at which it receives and forwards the packet to the next network segment. In this way, each bridge increases the COST value of its port to the COST value of the BPDU packets it receives. All bridges detect the COST value of their ports. The bridge with the lowest port COST value becomes the designated bridge. . A bridge with a higher port COST value sets its port into a blocked state and becomes a backup bridge. In the blocked state, a bridge stops forwarding, but it continues to receive and process BPDU packets.
The IEEE 802.1D specification includes Spanning Tree Algorithm (STA), which is a mechanism to ensure that forwarding loops never occur. STA uses Bridge Protocol Data Units (BPDU) to automatically configure independent ports on the bridge that are in the forwarding or blocking state. BPDU is a message sent by the bridge to a saved multicast MAC address (for Ethernet, this address is 01-80-C2-00-00-00), and all transparent bridges will listen to this address. In the blocking state, the port will not learn or forward the received frame. The end result of STA is a loopless bridge environment, regardless of whether the topology of the LAN segment changes, this environment always exists. The spanning tree algorithm determines the network link failure recovery time, at least 15 seconds.
The state of the spanning tree:
The port on the switch running the spanning tree protocol is always in one of the following five states:
Blocking: All ports start in a blocking state to prevent loops. The spanning tree determines which port is switched to the forwarding state. The port in the blocking state does not forward data frames but can accept BPDUs.
Monitoring: Does not forward data frames, but detects BPDU (temporary state).
Learning: Does not forward data frames, but learns the MAC address table (temporary state).
Forwarding: Data frames can be transmitted and received.
Disabled: Usually caused by port failure or switch configuration error.
3. Supreme-Ring Agreement
The Supreme-Ring protocol is a redundant mechanism used in industrial Ethernet. The Supreme-Ring protocol is somewhat similar to the Spanning Tree protocol. The Supreme-Ring protocol also defines a data packet, called a HELLO packet, also known as a WD packet (Watch Dog Packets). The switches use HELLO packet communication to dynamically select the main link and backup link on the main switch. But because there is only one path from the central bridge to any network segment, the bridge loop is eliminated.
In an industrial redundant ring network environment, the switch will not immediately start the forwarding function. The main switch (Local) is manually specified. The main link and the backup link are selected to establish a specified path, which is automatically specified by the Supreme-Ring protocol. There can be only one main switch (Local) in an industrial redundant ring network. The master switch (Local) will periodically send configuration information, which will be sent by all slave switches (Remote). Once the network structure changes, the network status will be reconfigured.
After specifying the main switch (Local), all ports are started in blocking mode before forwarding data packets. Using the Supreme-Ring algorithm, the main switch (Local) selects the port with the lowest COST value as the primary link, and the other port with the highest COST value as the backup link. The backup link does not forward data, only receives and processes HELLO packets, and is in a hot standby state. The slave switch (Remote) has no difference between the primary link and the backup link. The Supreme-Ring protocol is a simple and efficient redundant protocol, which can ensure that the ring network resumes network communication within 300ms when the link fails.
Supreme-Ring status:
The port on the switch running the Supreme-Ring protocol is always in one of the following four states:
Blocking: All ports are started in a blocked state to prevent loops. Ports in a blocked state do not forward data frames but can accept HELLO packets.
Hot Standby: Does not forward data frames, but learns the MAC address table, and enters the forwarding state immediately within 300ms when the main link fails.
Forwarding: Data frames can be transmitted and received.
Disabled: Usually caused by port failure or switch configuration error.
4 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 environments.
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 network bridged by a transparent bridge, a redundant path can establish a bridge loop, 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 switching network to prevent loops.
2. Spanning Tree Protocol
Spanning tree protocol is a mechanism commonly used in the IT world. Spanning tree protocol is a bridge nesting protocol, defined in the IEEE 802.1d specification, can be used to eliminate bridge loops. Its working principle is this: Spanning Tree Protocol defines a data packet, called Bridge Protocol Data Unit (BPDU). Bridges use BPDUs to communicate with each other, and use the related functions of BPDUs to dynamically select the root and backup bridges. But because there is only one path from the central bridge to any network segment, the bridge loop is eliminated.
In a spanning tree environment, bridges will not immediately start the forwarding function, they must first select a bridge as the root bridge, and then establish a designated path. The one 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 periodically send configuration information, 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.
When the root bridge is selected, before forwarding packets, they must decide on 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 All bridges are copied from their root ports. The root ports are those bridge ports connected to the root bridge. The information included in the BPDU is called the port COST. The network administrator assigns the port COST to all bridge ports. When the root bridge sends a BPDU, the root bridge sets its port value to zero. Then along this path, the next bridge increases its configuration port COST to a value, which is the value at which it receives and forwards the packet to the next network segment. In this way, each bridge increases the COST value of its port to the COST value of the BPDU packets it receives. All bridges detect the COST value of their ports. The bridge with the lowest port COST value becomes the designated bridge. . A bridge with a higher port COST value sets its port into a blocked state and becomes a backup bridge. In the blocked state, a bridge stops forwarding, but it continues to receive and process BPDU packets.
The IEEE 802.1D specification includes Spanning Tree Algorithm (STA), which is a mechanism to ensure that forwarding loops never occur. STA uses Bridge Protocol Data Units (BPDU) to automatically configure independent ports on the bridge that are in the forwarding or blocking state. BPDU is a message sent by the bridge to a saved multicast MAC address (for Ethernet, this address is 01-80-C2-00-00-00), and all transparent bridges will listen to this address. In the blocking state, the port will not learn or forward the received frame. The end result of STA is a loopless bridge environment, regardless of whether the topology of the LAN segment changes, this environment always exists. The spanning tree algorithm determines the network link failure recovery time, at least 15 seconds.
The state of the spanning tree:
The port on the switch running the spanning tree protocol is always in one of the following five states:
Blocking: All ports start in a blocking state to prevent loops. The spanning tree determines which port is switched to the forwarding state. The port in the blocking state does not forward data frames but can accept BPDUs.
Monitoring: Does not forward data frames, but detects BPDU (temporary state).
Learning: Does not forward data frames, but learns the MAC address table (temporary state).
Forwarding: Data frames can be transmitted and received.
Disabled: Usually caused by port failure or switch configuration error.
3. Supreme-Ring Agreement
The Supreme-Ring protocol is a redundant mechanism used in industrial Ethernet. The Supreme-Ring protocol is somewhat similar to the Spanning Tree protocol. The Supreme-Ring protocol also defines a data packet, called a HELLO packet, also known as a WD packet (Watch Dog Packets). The switches use HELLO packet communication to dynamically select the main link and backup link on the main switch. But because there is only one path from the central bridge to any network segment, the bridge loop is eliminated.
In an industrial redundant ring network environment, the switch will not immediately start the forwarding function. The main switch (Local) is manually specified. The main link and the backup link are selected to establish a specified path, which is automatically specified by the Supreme-Ring protocol. There can be only one main switch (Local) in an industrial redundant ring network. The master switch (Local) will periodically send configuration information, which will be sent by all slave switches (Remote). Once the network structure changes, the network status will be reconfigured.
After specifying the main switch (Local), all ports are started in blocking mode before forwarding data packets. Using the Supreme-Ring algorithm, the main switch (Local) selects the port with the lowest COST value as the primary link, and the other port with the highest COST value as the backup link. The backup link does not forward data, only receives and processes HELLO packets, and is in a hot standby state. The slave switch (Remote) has no difference between the primary link and the backup link. The Supreme-Ring protocol is a simple and efficient redundant protocol, which can ensure that the ring network resumes network communication within 300ms when the link fails.
Supreme-Ring status:
The port on the switch running the Supreme-Ring protocol is always in one of the following four states:
Blocking: All ports are started in a blocked state to prevent loops. Ports in a blocked state do not forward data frames but can accept HELLO packets.
Hot Standby: Does not forward data frames, but learns the MAC address table, and enters the forwarding state immediately within 300ms when the main link fails.
Forwarding: Data frames can be transmitted and received.
Disabled: Usually caused by port failure or switch configuration error.
4 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 environments.
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