Layer 2 | 577Far-end Failure DetectionFar-end Failure Detection is supported only on platform: eFar-end Failure Detection (FEFD) is a protocol that senses remote data link errors in a network. It respondsby sending a unidirectional report that triggers an echoed response after a specified time interval.Figure 25-10. Configuring Far-end Failure DetectionThe 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 intervalassumes that the far-end is not available. The connecting line protocol is brought down so that upper layerprotocols can detect the neighbor unavailability faster.FEFD state changesFEFD enabled systems (comprised of one or more interfaces) will automatically switch between fourdifferent modes: Idle, Unknown, Bi-directional, and Err-disabled.1. An interface on which FEFD is not configured is in Idle state.2. Once FEFD is enabled on an interface, it transitions to the Unknown state, and sends an FEFD packetto the remote end of the link.3. When the local interface receives the echoed packet from the remote end, the local interface transitionsto the Bi-directional state.4. If the FEFD enabled system is configured to use FEFD in Normal mode and neighboring echoes arenot received after three intervals, (each interval can be set between 3 and 300 seconds by the user) thestate changes to unknown.Force10(conf-if-gi-4/0)#show config!interface GigabitEthernet 4/0no ip addressswitchportfefdno shutdown Force10(conf-if-gi-1/0)#show config!interface GigabitEthernet 1/0no ip addressswitchportfefdno shutdownR1 R22w0d4h : FEFD packet sent via interface Gi 1/0Sender state -- Bi-directionalSender info -- Mgmt Mac(00:01:e8:14:89:25), Slot-Port(Gi 1/0)Peer info -- Mgmt Mac (00:01:e8:14:89:25), Slot-Port(Gi 4/0)Sender hold time -- 3 (second)R1 R22w0d4h : FEFD packet sent via interface Gi 4/0Sender state -- Bi-directionalSender info -- Mgmt Mac(00:01:e8:14:89:25), Slot-Port(Gi 4/0)Peer info -- Mgmt Mac (00:01:e8:14:89:25), Slot-Port(Gi 1/0)Sender hold time -- 3 (second)Keep-aliveEchoIntervalLayer2 001
