RFC 3619 (rfc3619) - Page 2 of 7

Extreme Networks' Ethernet Automatic Protection Switching (EAPS) Version 1

RFC 3619                 Extreme Networks' EAPS             October 2003


2.  Concept of Operation

   An EAPS Domain exists on a single Ethernet ring.  Any Ethernet
   Virtual Local Area Network (VLAN) that is to be protected is
   configured on all ports in the ring for the given EAPS Domain.  Each
   EAPS Domain has a single designated "master node".  All other nodes
   on that ring are referred to as "transit nodes".

   Of course, each node on the ring will have 2 ports connected to the
   ring.  One port of the master node is designated as the "primary
   port" to the ring, while the other port is designated as the
   "secondary port".

   In normal operation, the master node blocks the secondary port for
   all non-control Ethernet frames belonging to the given EAPS Domain,
   thereby avoiding a loop in the ring.  Existing Ethernet switching and
   learning mechanisms operate per existing standards on this ring.
   This is possible because the master node makes the ring appear as
   though there is no loop from the perspective of the Ethernet standard
   algorithms used for switching and learning.  If the master node
   detects a ring fault, it unblocks its secondary port and allows
   Ethernet data frames to pass through that port.  There is a special
   "Control VLAN" that can always pass through all ports in the EAPS
   Domain, including the secondary port of the master node.

   EAPS uses both a polling mechanism and an alert mechanism, described
   below, to verify the connectivity of the ring and quickly detect any
   faults.

2.1.  Link Down Alert

   When a transit node detects a link-down on any of its ports in the
   EAPS Domain, that transit node immediately sends a "link down"
   control frame on the Control VLAN to the master node.

   When the master node receives this "link down" control frame, the
   master node moves from the "normal" state to the ring-fault state and
   unblocks its secondary port.  The master node also flushes its
   bridging table, and the master node also sends a control frame to all
   other ring nodes, instructing them to flush their bridging tables as
   well.  Immediately after flushing its bridging table, each node
   begins learning the new topology.









Shah & Yip                   Informational