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Table Of Contents
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.
● In the unknown state, the interface starts transmitting link state information at a regular interval. The interface state
changes to bi-directional when a handshake is complete with the peer.
● When an interface is in bi-directional state, if it does not receive an echo from its peer for the time interval of three times
the configured FEFD message interval, the interface state changes to unknown in Normal mode. In Aggressive mode, the
interface state changes to err-disabled.
If the interface state changes to err-disabled, use the fefd reset [interface] global command to reset these interfaces.
The unknown or err-disabled state brings the line protocol down so that the protocols above it can detect that the peer link is
down.
Table 57. FEFD state changes
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