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fec (gigether)


Hierarchy Level


Supported on the following:

  • ACX6360-OX Transponders

  • ACX6360 routers

  • MX Series Routers with MPC7E, MPC8E, and MPC9E

  • MX10003 Router with MX10003 MPC

  • MX204 Router

  • PTX1000

  • FPC3-PTX-U2 and FPC3-PTX-U3 on PTX5000

  • QFX series switches

Enable or disable Reed-Solomon Forward Error Correction (RS-FEC) for a 100-Gigabit Ethernet interface. By default, the Junos OS software enables or disables FEC based on the plugged-in optics. For example, Junos OS enables RS-FEC for 100GbE SR4 optics and disables RS-FEC for 100GbE LR4 optics.

This statement allows you to override the default behavior and explicitly enable or disable RS-FEC. For example, you can extend the reach of 100GbE LR4 optics when you explicitly enable RS-FEC for the optics. RS-FEC is compliant with IEEE 802.3-2015 Clause 91.

Once you enable or disable RS-FEC using this statement, this behavior applies to any 100-Gigabit Ethernet optical transceiver installed in the port associated with the interface.

You can configure forward error correction (FEC) clauses CL74 on 25-Gigabit and 50-Gigabit interfaces, and CL91 on 100-Gigabit interfaces. Since the FEC clauses are applied by default on these interfaces, you must disable the FEC clauses if you do not want to apply them.


FPC-PTX-P1-A and FPC2-PTX-P1A on PTX5000 routers do not support RS-FEC.

FPC3-SFF-PTX-1H and FP3-SFF-PTX-1T with PE-10-U-QSFP28 PIC and LR4 optics on PTX3000 and PTX5000 routers supports RS-FEC only on port 2. For PE-10-U-QSFP28 with LR4 optics, RS-FEC is the default FEC mode on port 2 and NONE is the default FEC mode on ports 0,1,3 through 9. For PE-10-U-QSFP28 with SR4 optics, RS-FEC is enabled by default on all ports. Do not modify the FEC mode on any port irrespective of the optics installed.

To check the FEC status, use the show interfaces interface-name command.


Junos OS software automatically enables or disables RS-FEC based on the type of pluggable optics used.



Enables RS-FEC. RS-FEC is compliant with IEEE 802.3-2015 Clause 91.


Enables RS-FEC. RS-FEC is compliant with IEEE 802.3-2015 Clause 74.


Disables RS-FEC.

Required Privilege Level

interface—To view this statement in the configuration.

interface-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 16.1R1