Install Guide

Far-End Failure Detection
Far-end failure detection (FEFD) is a protocol that senses remote data link errors in a network. FEFD responds by sending a
unidirectional report that triggers an echoed response after a specified time interval. You can enable FEFD globally or locally on
an interface basis. Disabling the global FEFD configuration does not disable the interface configuration.
Figure 74. Configuring Far-End Failure Detection
The report consists of several packets in SNAP format that are sent to the nearest known MAC address.
In the event of a far-end failure, the device stops receiving frames and, after the specified time interval, assumes that the
far-end is not available. The connecting line protocol is brought down so that upper layer protocols can detect the neighbor
unavailability faster.
FEFD State Changes
FEFD has two operational modes, Normal and Aggressive.
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. When you enable Aggressive mode on an interface in the same state,
manual intervention is required to reset the interface.
FEFD enabled systems (comprised of one or more interfaces) automatically switches between four different states: Idle,
Unknown, Bi-directional, and Err-disabled.
1. An interface on which FEFD is not configured is in Normal mode by default.
2. After you enable FEFD on an interface, it transitions to the Unknown state and sends an FEFD packet to the remote end of
the link.
3. When the local interface receives the echoed packet from the remote end, the local interface transitions to the Bi-directional
state.
4. If the FEFD enabled system is configured to use FEFD in Normal mode and neighboring echoes are not received after three
intervals, (you can set each interval can be set between 3 and 300 seconds) the state changes to unknown.
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