Cisco Catalyst 8500 and 8500L Series Edge Platforms Software Configuration Guide

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Configure Forward Error Correction

Updated: February 6, 2026

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Overview

Forward Error Correction checks and recovers potential errors during long-range data transmission.

Forward Error Correction checks and recovers potential errors during long-range data transmission. Because the Cisco Catalyst 8500L Edge Platforms have long-range SFP, FEC must be configured.

Follow these steps to configure Forward Error Correction:

Procedure

1.

enable source-interface gigabitethernet slot/port

Example:


Router# enable

Enables the privileged EXEC mode. If prompted, enter your password.
2.

configure terminal

Example:


Router# configure terminal

Enters the global configuration mode.
3.

interface twentyfivegigabitethernet slot/port

Example:


Router(config)# interface twentyfivegigabitethernet0/0/164/11

Specifies the 25-gigabit Ethernet interface to be configured.

Here:

slot/port specifies the location of the interface.
4.

fec { auto | cl108 | cl74 | off }

Example:


Router(config)#  fec cl74-fc

Configuring fec cl74 enables Clause 74 FC-FEC on the interface, which helps correct errors in the data stream to maintain signal integrity and performance.

The fec command supports these modes:

  • auto—Enables FEC based on SFP type

  • cl108—Enables clause108 <= RS-FEC(528,514)

  • cl74—Enables clause74 <= FC-FEC

  • disable—Disables FEC on interface

Note

  • The fec command is only applicable to 25G links.

  • For 10- or 25-Gbps dual-rate SFP modules, if the speed changes from 25 Gbps to 10 Gbps, remove the fec configuration before changing the speed.