Cisco SFP-25G-SR-S optics on ACI 9300-EX Leafs

[vv0bbLeS]

Hello all,

I'm trying to determine if Cisco's 25-gig optics (e.g. SFP-25G-SR-S) are OK to use on 9300-EX series leafs (or even all ACI leafs in general).

Reading the Data Sheet for the 25-gig SFP's, one of the main things I notice is that all the 25-gig optics are S-class optics, and in the description of each I read that this module requires RS-FEC on the host ports

• This RS-FEC requirement can also be seen in the short Cisco publication on 25-Gigabit Pluggable Transceivers for Data Center Applications, in the section Forward Error Correction (FEC) For 25G transceivers .
• This RS-FEC requirement is also discussed in the even shorter Cisco publication Don't Mix Up Your FECs
• We can also see in the brief FEC Summary Table that the SFP-25G-SR-S only supports RS-FEC and doesn't support FC-FEC like other 25-gig transceivers do (e.g. SFP-10/25G-CSR-S).

Now, on the switch side of things, looking at the Data Sheet for Cisco 9300-EX Series switches, I read that the Cisco Nexus 93180YC-EX switch has the "other" FEC mode of FC-FEC (Fire Code FEC) enabled for 25-gig. So from all I've read, this 93180YC-EX model of leaf should not work with the SFP-25G-SR-S transceiver, because that switch model doesn't have the RS-FEC mode that those SFP-25G-SR-S SFP's require.

However, before I had researched all this, I used those exact SFP-25G-SR-S optics on a Cisco Nexus 93180YC-EX switch to connect some HP servers, and from all I can tell those optics are working just fine on that -EX switch, which doesn't make sense based on all that I've read above.

So, my question is, is the requirement for RS-FEC a "hard" requirement on the SFP-25G-SR-S optics, or more of a "recommendation" ? ( From my personal experience here, it appears it's more of a "recommendation" and if so I could continue using them on my -EX switches ?)

[Oliver Qiu]

Hi,

Your research is correct. 93180YC-EX doesn't support RS-FEC mode and SFP-25G-SR-S transceiver. 

Regrettably, do not possess any records that support your claims. Nonetheless, it is important to mention that the optics are not compatible with this platform. Although they might work in your setting, we advise keeping a close watch on their effectiveness. If any problems arise, such as instability or disruption of traffic, the Technical Assistance Center (TAC) will most likely recommend replacing the SFPs as the initial step. It is also crucial to note that developers do not focus on unsupported situations, so please take that into account.

You can also check below Cisco Optics-to-Device Compatibility Matrix

https://tmgmatrix.cisco.com/?si=93180YC-EX 

https://tmgmatrix.cisco.com/?si=SFP-25G-SR-S 

[Alexei Monastyrnyi]

Hi Oliver.

"does not support RS-FEX" means it will be working without RS-FEX feature as 25G, is it?