[Basic Networking] Overview of ERPS

Hi, community!!

This time I will share an introduction to a protocol very useful in eliminating loops at Layer 2. That protocol is ERPS. Hope you like it!!

Definition

ERPS (Ethernet Ring Protection Switching) is a protocol defined by the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) to eliminate loops at Layer 2. Because the standard number is ITU-T G.8032/Y1344, ERPS is also called G.8032. ERPS defines Ring Auto Protection Switching (RAPS) Protocol Data Units (PDUs) and protection switching mechanisms.

ERPS has two versions: ERPSv1 released by ITU-T in June 2008 and ERPSv2 released in August 2010. EPRSv2, fully compatible with ERPSv1, provides the following enhanced functions:

·         Multi-ring topologies, such as intersecting rings

·         RAPS PDU transmission on non-virtual-channels (NVCs) in sub-rings

·         Forced Switch (FS) and Manual Switch (MS)

·         Revertive and non-revertive switching

Purpose

Generally, redundant links are used on an Ethernet switching network such as a ring network to provide link backup and enhance network reliability. The use of redundant links, however, may produce loops, causing broadcast storms and rendering the MAC address table unstable. As a result, communication quality deteriorates, and communication services may even be interrupted. Table 1 describes ring network protocols supported by devices.

Ethernet networks demand faster protection switching. STP does not meet the requirement for fast convergence. ERPS, a standard ITU-T protocol, prevent loops on ring networks. It optimizes detection and performs fast convergence. ERPS allows all ERPS-capable devices on a ring network to communicate.

Benefits:

·         Prevents broadcast storms and implements fast traffic switchover on a network where there are loops.

·         Provides fast convergence and carrier-class reliability.

·         Allows all ERPS-capable devices on a ring network to communicate.

Application Scenarios for ERPS

Generally, redundant links are used on an Ethernet switching network to provide link backup and enhance network reliability. The use of redundant links, however, may produce loops, causing broadcast storms and rendering the MAC address table unstable. As a result, communication quality deteriorates, and communication services may even be interrupted.

To prevent loops caused by redundant links, enable ERPS on the nodes of the ring network. ERPS is a Layer 2 loop-breaking protocol defined by the ITU-T, and provides fast convergence of carrier-class reliability standards.

Figure 1 Layer 2 application of ERPS

As shown in Figure 1, SwitchA through SwitchE constitute a ring. The ring runs ERPS to provide protection switching for Layer 2 redundant links and prevent loops that cause broadcast storms and render the MAC address table unstable.

Generally, the Ring Protection Link (RPL) owner port is blocked and does not forward service packets, preventing loops. If a fault occurs on the link between SwitchA and SwitchB, ERPS will unblock the blocked RPL owner port and traffic from User network1 and User network2 is forwarded through the path SwitchC ->SwitchD ->SwitchE.

That`s all!!

Hope you find my post useful. Please let me know in the Comment Section if you have any further concerns or remarks.

Thank you!

Source: https://support.huawei.com/hedex/hdx.do?docid=EDOC1100136523&lang=en&id=EN-US_CONCEPT_0141111827

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