Ethernet Automatic Protection System

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Ethernet Automatic Protection System is used to create a fault tolerant topology by configuring a primary and secondary path for each VLAN.

It was invented by Extreme Networks. The idea is to provide highly available Ethernet switched rings (commonly used in Metro Ethernet ).

[edit] Operation

A ring is formed by configuring a Domain. Each domain has a single "master node" and many "transient nodes". Each transient node will have a primary port and a secondary port, both known to be able to direct traffic to the master node. Under normal operation only the primary port is used to avoid loops (the secondary port is blocked for all non-control traffic). When there a link down situation, the master unblocks the secondary port and instructs all its nodes to re-learn the topology.

The same switch can belong to multiple domains, thus multiple rings. However, these act as independent entities.

EAPS v2

EAPSv2 is configured and enabled to avoid the potential of super loops in environments where multiple EAPS domain share a common link. EAPSv2 works using the concept of controller and partner mechanism. Shared port status is verified using health PDUs exchanged by controller and partner. When a shared link goes down, the configured Controller will open only one segment port for each of the protected VLANs, keeping all other segment ports in a blocking state. These states will be maintained as long as Controller keeps receiving health PDU on the open segment ports from Partner. If health check PDUs are not received on open segment port due to transient loop in any of the domain, the Controller will falsely deduce that the segment is down and take an action to open one of the remaining blocked segment ports. This introduces a super loop if the protect vlans share multiple EAPS domains.