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25G Ethernet Consortium and/or IEEE standard

Walter Dey
VIP Alumni
VIP Alumni

Are the Cisco Nexus 93180YC-FX 25G ports compliant with the 25G Consortium and/or IEEE standard ?

6 Replies 6

cweinhold
Level 4
Level 4

I'm not sure if the 93180YC-FX is fully 802.3by-compliant, but it does support RS-FEC.

 

25G Ethernet requires forward error correction (FEC) everywhere but 1 & 2-meter passive copper cables. There are two 25G Ethernet FEC algorithms:

  • FC-FEC (aka "FireCode" or "BASE-R" or "Clause 74") offers simple, low-latency (< 100ns) protection against bursty errors, but is not so good for random errors. It's used on 3 and 5-meter passive copper cables, and on active optical 25G cables up to 10 meters.   (it's also used on every 100G interface)
  • RS-FEC (aka "Reed Solomon" or "Clause 91" or "Clause 108") offers better error protection but adds latency (~250ns). It is required for the 25G MMF transceivers (Cisco p/n SFP-25G-SR-S) for distances up to 100 meters. I suspect it might also be needed on active optical cables over 10 meters long (if Cisco sold them).

Every 25G device supports FC-FEC, but RS-FEC is newer and more rare. E.g., the Nexus 9300-FX is Cisco's first switch to support RS-FEC. QLogic's QL4521x doesn't do RS-FEC, but their QL41212 apparently does.

 

Product incompatibility will be a minor headache, but autonegotiation could be what we curse in the future! The IEEE struggled with adapting autonegotiation for FEC, and many early 25G products may not understand the negotiation from the final 802.3by draft. I expect a lot of vendor interop issues with FEC negotiation, and a lot of frustrated end-users who resort to hardcoding it.

 

[Update Nov 2018] Do check out Cisco's new SFP-10/25G-CSR-S transceiver. With two, it claims 70/100 meters (OM3/OM4) with FC-FEC  and 30/50 meters without any FEC. It also interoperates over regular distances with standard 10G and 25G-SR transceivers.

Just as an update,

QL45212 and Nexus 9508

In order to get the link to fire, i needed to turn fec off on the Nexus side.  Any other fec or auto negotiation failed to link.

I had same issues with cisco Nexus9000 C93180LC-EX connecting to a Dell Compellent Storage Center.  I had to hard set both sides to 25GB and turn FEC off on the Nexus switch.

All the 3.2 train releases had a bug until 3.2.3o which caused issues with 25Gb negotiation. This bug was resulting in unstable or no link unless FEC was disabled in a deployment with 93180YC-EX and Broadcom 57414 NICs.

 

See CSCvm46784. If you are on an earlier 3.2 I would consider upgrading.

Oh my god! Thank you @richmond !!

We have just deployed our new datacenter based on Nexus 93180YC-EX and was connecting a pair of Dell servers with 57414 NICs without luck. I think we tried all settings except turning off FEC on the switch.. Seems like this bug is there on 9.2(3) software...

The only FEC setting i was able to use was fc-fec, rs-fec (or any other for that matter)  results in; ERROR: FEC validation failed on ethx/xx due to incompatible configured speed or transceiver type
We are running generic cisco-coded SFP-10/25G-CSR-S in the Nexuses and generic (one dell 407-bbwk coded and one MSA-Standard coded) SFP-25G-SR-S in the Dell server.

Hi Andreas. Glad it helped. 

 

We also had to upgrade the server firmware as there were bugs in the Broadcom NIC behaviour as well. Try updating the server firmware.

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