Extreme Networks ExtremeWare XOS Guide Manual page 268

Ethernet Automatic Protection Switching
An Ethernet ring built using EAPS can have resilience comparable to that provided by SONET rings, at
a lower cost and with fewer restraints (such as ring size). The EAPS technology developed by Extreme
Networks to increase the availability and robustness of Ethernet rings is described in RFC 3619: Extreme
Networks' Ethernet Automatic Protection Switching (EAPS) Version 1.
EAPS operates by declaring an EAPS domain on a single ring. Any virtual LAN (VLAN) that warrants
fault protection is configured on all ring ports in the ring, and is then assigned to an EAPS domain. On
that ring domain, one switch, or node, is designated the master node (see Figure 14), while all other
nodes are designated as transit nodes.
Figure 13: Gigabit Ethernet fiber EAPS MAN ring
Transit
node
Transit
node
Transit
Gigabit Ethernet Fiber node
EAPS MAN ring
Transit
node
Master
node
EW_070
One port of the master node is designated the master node's primary port (P) to the ring; another port is
designated as the master node's secondary port (S) to the ring. In normal operation, the master node
blocks the secondary port for all non-control traffic belonging to this EAPS domain, thereby avoiding a
loop in the ring, like STP. Layer 2 switching and learning mechanisms operate per existing standards on
this ring.
NOTE
Like the master node, each transit node is also configured with a primary port and a secondary port on the ring, but
the primary/secondary port distinction is ignored as long as the node is configured as a transit node.
268
ExtremeWare XOS 11.1 Concepts Guide