Restoring Normal Operation, Master Node

How EPSR Works

Restoring Normal Operation

Master Node

Once the fault has been fixed, the master node’s Health messages traverse the whole ring and arrive at the master node’s secondary port. The master node then restores normal conditions by:

1.declaring the ring to be in a state of Complete

2.blocking its secondary port for data VLAN traffic (but not for the control VLAN)

3.flushing its forwarding database for its two ring ports

4.sending a Ring-Up-Flush-FDB message from its primary port, to all transit nodes.

Transit Nodes with One Port Down

As soon as the fault has been fixed, the transit nodes on each side of the (previously) faulty link section detect that link connectivity has returned. They change their ring port state from Links Down to Pre-Forwarding, and wait for the master node to send a Ring-Up-Flush-FDB control message.

Once these transit nodes receive the Ring-Up-Flush-FDB message, they:

•flush the forwarding databases for both their ring ports

•change the state of their ports from blocking to forwarding for the data VLAN, which allows data to flow through their previously-blocked ring ports

The transit nodes do not start forwarding traffic on the previously-down ports until after they receive the Ring-Up-Flush-FDB message. This makes sure the previously-down transit node ports stay blocked until after the master node blocks its secondary port. Otherwise, the ring could form a loop because it had no blocked ports.

Transit Nodes with Both Ports Down

The Allied Telesis implementation includes an extra feature to improve handling of double link failures. If both ports on a transit node are down and one port comes up, the node:

1.puts the port immediately into the forwarding state and starts forwarding data out that port. It does not need to wait, because the node knows there is no loop in the ring— because the other ring port on the node is down

2.remains in the Links Down state

3.starts a DoubleFailRecovery timer with a timeout of four seconds

4.waits for the timer to expire. At that time, if one port is still up and one is still down, the transit node sends a Ring-Up-Flush-FDB message out the port that is up. This message is usually called a “Fake Ring Up message”.

Sending this message allows any ports on other transit nodes that are blocking or in the Pre- forwarding state to move to forwarding traffic in the Links Up state. The timer delay lets the device at the other end of the link that came up configure its port appropriately, so that it is ready to receive the transmitted message.

Note that the master node would not send a Ring-Up-Flush-FDB message in these circumstances, because the ring is not in a state of Complete. The master node’s secondary port remains unblocked.

Page 7 AlliedWare™ OS How To Note: EPSR

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.