Users Guide

Far-end failure detection
Far-End Failure Detection (FEFD) is a protocol that detects remote data link errors in a network.
FEFD uses a link layer echo protocol to detect and signal far-end failures over Ethernet and optical links. When you enable
FEFD, switches periodically exchange FEFD echo frames to identify link failures. If the local switch does not receive an echo
from its peer for the time interval of three times the configured FEFD message interval, the local switch assumes that the peer
link is down. The default interval for FEFD message interval is 15 seconds. For example, with the default configuration, if the
local switch does not receive an echo message for 45 seconds from its peer, it brings the peer link down.
FEFD helps detect far-end failure when the following problems occur:
● Only one side receives packets although the physical layer (L1) of the link is up on both sides.
● Transceivers are not connected to the correct ports.
FEFD states
FEFD comprises the following four states:
● Idle—FEFD is disabled.
● Unknown—Shown when FEFD is enabled and changes to bi-directional after successful handshake with the peer.
Also shown if the peer goes down in normal mode.
● bi-directional—Interface is up, connected, and receiving echoes of its neighbor.
● err-disabled—Only found when FEFD mode is aggressive and when the interface has not received three echoes of
its neighbor. To reset an interface in this state, use the fefd reset command.
FEFD modes
FEFD operates in two modes—Normal mode and aggressive mode.
● Normal mode—When you enable Normal mode on an interface and a far-end failure is detected, no intervention is required
to reset the interface to bring it back to an FEFD operational state.
● Aggressive mode—When you enable Aggressive mode on an interface in the same state, you must manually reset the
interface.
The following events explain how FEFD state transition occurs:
● When you enable FEFD on an interface a link transitions from idle state to unknown state.
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