Extreme Networks 200 Series - Manual (Page 146)

144 Summit 200 Series Switch Installation and User Guide
Ethernet Automatic Protection Switching
EAPS protection switching is similar to what can be achieved with the Spanning Tree Protocol (STP),
but offers the advantage of converging in less than a second when a link in the ring breaks.
NOTE
In order to use EAPS, you must enable EDP on the switch. For more information on EDP, refer to
Chapter 6.
EAPS operates by declaring an EAPS domain on a single ring. Any 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 26), while all other nodes are
designated as transit nodes. A stacked configuration appears as a single node on the EAPS ring and
may serve as the master node or as a transit node.
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.
Figure 26: EAPS operation
If the ring is complete, the master node logically blocks all data traffic in the transmit and receive
directions on the secondary port to prevent a loop. If the master node detects a break in the ring, it
unblocks its secondary port and allows data traffic to be transmitted and received through it.
EW_071
Direction of
health-check
message Master
node
Secondary port
is logically blocked
S 4
S 5
S 6
S 3
S 2
S 1
S P