Allied Telesis EPSR AT-8948 User Manual
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AlliedWareTM OS

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


Putting a ring of Ethernet switches at the core of a network is a simple way to increase the network’s resilience—sucha network is no longer susceptible to a single point of failure. However, the ring must be protected from Layer 2 loops. Traditionally,STP-basedtechnologies 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—withinas 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-stepconfiguration 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

C613-16092-00REV D

Which products and software versions does it apply to?

"Example 3: EPSR and RSTP" on page 17

"Example 4: EPSR with Nested VLANs" on page 20

"Example 5: EPSR with management stacking" on page 23

"Example 6: EPSR with an iMAP" on page 26

Next, it discusses important implementation details in the following sections:

"Classifiers and Hardware Filters" on page 29

"Ports and Recovery Times" on page 30

"IGMP Snooping and Recovery Times" on page 31

"Health Message Priority" on page 31

Finally, it ends with troubleshooting information in the following sections:

"EPSR State and Settings" on page 32

"SNMP Traps" on page 34

"Counters" on page 35

"Debugging" on page 36

Which products and software versions does it apply to?

This How To Note applies to the following Allied Telesis switches:

AT-8948,x900-48FE,x900-48FE-N,AT-9924T,AT-9924SP,andAT-9924T/4SPswitches, running software version 2.8.1 or later

AT-9924Ts,x900-24XT,andx900-24XT-Nswitches running software version 3.1.1 or later

EPSR is also available on the following Allied Telesis switches, running the AlliedWare Plus OS software version 5.2.1 or later:

SwitchBlade x908

x900 series

For information about using the AlliedWare Plus OS, see the AlliedWare Plus Note, How To Configure EPSR (Ethernet Protection Switching Ring) to Protect a Ring from Loops. This Note is available

The implementation on the above switches is also compatible with EPSR on Allied Telesis’ Multiservice Access Platforms (iMAPs).

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