Error-Correction FEC Arista - Cisco Interconnect

Netmart · ‎07-16-2025

I just want share my experience when setting up a connection between Cisco 25GB SR and Arista [100GB Breakout, 4x 25GB]

For both sites to be able to successfully negotiate the physical layer parameters the following is required.

Cisco works with auto [default] or cl174 while Arista needs to be set up as encoding fire-code.

Cisco		Arista
Options
cl74 cl91 Auto [default]		error-correction encoding fire-code
		error-correction Reed-Solomon
Media
CISCO-FINISAR SFP-H25GB-SR		100GBASE-SR4 [breakout, 4x 25GB]

==================================

Cisco, 93180YC-EX

interface Ethernet1/47

description Arista-DCS-7508N E8/21/3

switchport monitor

fec cl74

93180YC-EX # sh int ethernet 1/47

Ethernet1/47 is up

admin state is up, Dedicated Interface

Hardware: 1000/10000/25000 Ethernet, address: 70df.2fe6.f4e8 (bia 70df.2fe6.f4e8)

description Arista-DCS-7508N: E8/21/3

MTU 1500 bytes, BW 25000000 Kbit, DLY 10 usec

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, medium is broadcast

Port mode is access

full-duplex, 25 Gb/s, media type is 25G

Beacon is turned off

Auto-Negotiation is turned off, FEC mode is CL74

Input flow-control is off, output flow-control is off

Auto-mdix is turned off

Rate mode is dedicated

Switchport monitor is on

EtherType is 0x8100

==============================

Arista-DCS-7508N:

interface Ethernet8/21/3

description Cisco, 93180YC-EX, E1/47

error-correction encoding fire-code

switchport mode tap

switchport tap default group mtnbox_nt0-AlwaysOn group mtsniff01_enp131s0f0-A

DCS-7508N#sh int ethernet 8/21/3 error-correction

Interface Configured Available Operational

---------------- -------------------- ---------------------------------------------------- -----------

Ethernet8/21/3 Fire-code Reed-Solomon, Fire-code Fire-code

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