Concept Guide

In the event of a far-end failure, the device stops receiving frames and, after the specied 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 dierent states: Idle, Unknown, Bi-
directional, and Err-disabled.
1 An interface on which FEFD is not congured 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 congured 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.
5 If the FEFD system has been set to Aggressive mode and neighboring echoes are not received after three intervals, the state changes
to Err-disabled. You must manually reset all interfaces in the Err-disabled state using the fefd reset [interface] command in
EXEC privilege mode (it can be done globally or one interface at a time) before the FEFD enabled system can become operational
again.
Table 33. State Change When Conguring FEFD
Local Event Mode Local State Remote State Local Admin
Status
Local Protocol
Status
Remote Admin
Status
Remote
Protocol
Status
Shutdown Normal Admin
Shutdown
Unknown Down Down Up Down
Shutdown Aggressive Admin
Shutdown
Err-disabled Down Down Up Down
FEFD enable Normal Bi-directional Bi-directional Up Up Up Up
FEFD enable Aggressive Bi-directional Bi-directional Up Up Up Up
FEFD + FEFD
disable
Normal Locally disabled Unknown Up Down Up Down
FEFD + FEFD
disable
Aggressive Locally disabled Err-disabled Up Down Up Down
Link Failure Normal Unknown Unknown Up Down Up Down
Link Failure Aggressive Unknown Unknown Up Down Up Down
Important Points to Remember
• FEFD enabled ports are subject to an 8 to 10 second delay during an RPM failover before becoming operational.
• You can enable FEFD globally or on a per-interface basis. Interface FEFD congurations override global FEFD congurations.
• Dell EMC Networking OS supports FEFD on physical Ethernet interfaces only, excluding the management interface.
• FEFD is not supported on Fibre Channel and copper Ethernet ports.
Layer 2
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