40GbE ConnectX-4 to ConnectX-3 Transceiver Recommendation

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New Member
Oct 25, 2023
tl;dr - I'm trying to connect a ConnectX-4 MCX4131A-BCAT to a ConnectX-3 MCX354A at 40GbE. My Kaiam XQX2502's only seem to negotiate 1GbE. Is there a transceiver that will get me back to 40Gbps?

Previously, I had two ConnectX-3 MCX354A's connected (Windows to Linux) with Kaiam XQX2502's linked at 40GbE and all was well until I swap one of the machines for Intel's Alder Lake and discovered that ConnectX-3's Windows Driver BSOD's with Alder Lake's E-Cores.

No big deal, I'll just upgrade the Alder Lake machine's card to a ConnectX-4 MCX4131A-BCAT, which is what I did and was able to boot on Windows with all the E cores enabled.

However, with the XQX2502, the two cards were only able to negotiate 1 Gbps. I tried forcing 40 Gbps as suggested by some other site, but wasn't able to with the latest WinOF2. I was able to find a version (2.0.51100) that could set the speed, but that resulted in a failure to link.

Then I find on this forum that apparently the XQX2502's and ConnectX-4 don't play together nicely.

Is there a transceiver that works with both the MCX354A, MCX4131A, and will link via SMF with LC-LC connections at 40Gbps available at a low cost?
Thanks for any recommendations!