How can I connect a QSFP28 card to RJ45-based network equipment?

[kingmouf]

Hi all,

I am developing a hardware design on an Alveo U55C card (Alveo U55C High Performance Compute Card) and need some basic network functions. However, I can only use the QSFP28 interfaces that the board provides, yet all lab equipment that I can connect it to is copper RJ45. An initial google search provides multiple results for SFP -> RJ45 breakout cables, however I didnt really find anything useful for QSFP28 to RJ45. I noticed on forums that some people mention a two stage conversion from QSFP28 to SFP+ and then from that to RJ45, however to me this seems like too unprobable to work. Buying cables and converters is not that cheap of an experiment, so if anyone has any experience or has tried it, I would appreciate it a lot. (please note that performance is irrelevant for my application. I just need it to work, so that I can establish some kind of communication).

Thank you in advance,
Andreas

 

[bitbckt]

QSFP (quad) to SFP is purely passive and mechanical: a four lane signaling interface is reduced to a single lane. There’s nothing complicated about it. SFP to RJ45 is an active conversion, but the source of the single lane is irrelevant.

Assuming there isn’t any transceiver vendor ID shenanigans going on, there is very little reason at all why that wouldn’t work just fine.

 

[kingmouf]

This was fast! Thank you! So you are saying that a solution like this:
Alveo Card QSFP28 -> https://www.fs.com/de-en/products/116272.html?attribute=10175&id=2293723 -> 10G BASE-T RJ45 SFP+ Module -> cat6a cable -> our RJ45 based switch, should work?

 

[bitbckt]

No, use something like this in the port: https://www.fs.com/products/72588.html

You don’t need a breakout cable if only a single lane is needed.

 

[nexox]

Note that most network cards don't support those breakout cables, they're typically used with switches (and still not all switches with QSFP ports are compatible.) If you're ok shopping used for the passive QSFP->SFP adapter then a good search term is "QSA", which is what Mellanox calls them.

 

[i386]

a good search term is "QSA", which is what Mellanox calls them.

QSA for the "older" 40GBE to 10GBE conversion
QSA28 for the newer 100GBE to 25GBE conversion

 

[kingmouf]

Thank you all guys!! This forum is amazing!