Allied Telesis AT-9924T/4SP-A-20, AT-8948 manual Introduction, Restoring Normal Operation on page

AlliedWareTM OS

How To Configure EPSR (Ethernet Protection Switching Ring) to Protect a Ring from Loops

Introduction

Putting a ring of Ethernet switches at the core of a network is a simple way to increase the network’s resilience—such a network is no longer susceptible to a single point of failure. However, the ring must be protected from Layer 2 loops. Traditionally, STP-based technologies are used to protect rings, but they are relatively slow to recover from link failure. This can create problems for applications that have strict loss requirements, such as voice and video traffic, where the speed of recovery is highly significant.

This How To Note describes a fast alternative to STP: Ethernet Protection Switching Ring (EPSR). EPSR enables rings to recover rapidly from link or node failures—within as little as 50ms, depending on port type and configuration. This is much faster than STP at 30 seconds or even RSTP at 1 to 3 seconds.

What information will you find in this document?

This How To Note begins by describing EPSR in the following sections:

•"How EPSR Works" on page 3

•"Establishing a Ring" on page 4

•"Detecting a Fault" on page 5

•"Recovering from a Fault" on page 5

•"Restoring Normal Operation" on page 7

Next it gives step-by-step configuration details and examples in the following sections:

•"How To Configure EPSR" on page 8

•"Example 1: A Basic Ring" on page 11

•"Example 2: A Double Ring" on page 14

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