How EPSR Works

Establishing a Ring

Once you have configured EPSR on the switches, the following steps complete the EPSR ring:

1.The master node creates an EPSR Health message and sends it out the primary port. This increments the master node’s Transmit: Health counter in the show epsr count command.

2.The first transit node receives the Health message on one of its two ring ports and, using a hardware filter, sends the message out its other ring port.

Note that transit nodes never generate Health messages, only receive them and forward them with their switching hardware. This does not increment the transit node’s Transmit: Health counter. However, it does increment the Transmit counter in the show switch port command.

The hardware filter also copies the Health message to the CPU. This increments the transit node’s Receive: Health counter. The CPU processes this message as required by the state machines, but does not send the message anywhere because the switching hardware has already done this.

3.The Health message continues around the rest of the transit nodes, being copied to the CPU and forwarded in the switching hardware.

4.The master node eventually receives the Health message on its secondary port. The master node's hardware filter copies the packet to the CPU (which increments the master node’s Receive: Health counter). Because the master received the Health message on its secondary port, it knows that all links and nodes in the ring are up.

When the master node receives the Health message back on its secondary port, it resets the Failover timer. If the Failover timer expires before the master node receives the Health message back, it concludes that the ring must be broken.

Note that the master node does not send that particular Health message out again. If it did, the packet would be continuously flooded around the ring. Instead, the master node generates a new Health message when the Hello timer expires.

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Allied Telesis AT-9924SP-30, X900-48FE-N, AT-9924T/4SP-A-20, AT-8948, AT-9924T-40 manual Establishing a Ring
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AT-9924SP-30, AT-9924T-40, AT-8948, AT-9924T/4SP-A-20, X900-48FE-N specifications

Allied Telesis is a leading provider of networking solutions, renowned for its innovative technologies and high-performance networking equipment. Among its extensive product lineup, the X900-48FE-N, AT-9924T-40, AT-8948, AT-9924T/4SP-A-20, and AT-9924SP-30 stand out for their remarkable features and capabilities.

The X900-48FE-N is a robust layer 2/3 managed switch that features 48 Fast Ethernet ports. This model is particularly known for its energy efficiency and reliability, making it a suitable choice for enterprises with demanding networking needs. It supports a wide range of Layer 2 Ethernet switching technologies, including VLANs, Spanning Tree Protocol (STP), and Link Aggregation Control Protocol (LACP), which enhances network reliability and efficiency.

The AT-9924T-40 is a versatile switch designed for high-performance environments. It offers a rich set of features, including 24 Gigabit Ethernet ports and 4 SFP ports for fiber connectivity. This device is equipped with Advanced Layer 2 and Layer 3 features, including IPv4/IPv6 support, Quality of Service (QoS) capabilities, and robust security options. This switch is ideal for core and distribution deployments within enterprise networks, ensuring fast and reliable connectivity.

The AT-8948 is another important model in Allied Telesis' offerings. It features 48 10/100 Mbps Ethernet ports and 4 Gigabit uplink ports, providing a high density of connectivity options. The AT-8948 is also equipped with advanced management capabilities, including SNMP, RMON, and web-based management, allowing for easy configuration and monitoring of the network.

The AT-9924T/4SP-A-20 offers a combination of 24 Gigabit Ethernet ports and 4 SFP slots to extend network capabilities through fiber connections. It is particularly well-suited for environments requiring high bandwidth and flexible connectivity. Its compact design makes it an excellent choice for data centers and enterprise networks.

Lastly, the AT-9924SP-30 is characterized by its 24 Gigabit SFP ports, offering flexibility in terms of fiber connectivity. This switch supports advanced routing capabilities and is designed for high-availability environments. Its ability to handle diverse network traffic while maintaining optimal performance makes it a valuable asset for any modern enterprise.

In summary, these Allied Telesis models showcase advanced features, network reliability, and versatile management options, making them critical components for efficient and scalable networking solutions.
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