Well, hate to tell you but you'll be limited 10Gb/s with these Intel cards because they require FEC.
Where can I read more about FEC (forward error correction?) and how that affects link speeds?
The specific 25G optic is https://www.flexoptix.net/en/p-b1625g-10-ad.html?co10426=972... and indeed does not support FEC.
The remote end is a Cisco C9500-48Y4C, on which one can turn off FEC.
On the Intel side, I found https://www.intel.com/content/dam/www/public/us/en/documents..., which mentions that while No-FEC might result in “poor link quality” (sure, that’s why people use FEC), it does not say anything about degraded mode or limits to 10G.
By controller datasheet, I take it you’re referring to https://www.mouser.cn/datasheet/2/612/710_series_datasheet_v...
That document contains a state machine diagram listing 25G AUI‐RS, 25G AUI‐FC and 25G AUI‐N (in order) before the fallback to 10G SFI.
Did you misread or am I missing something?
In either case, I’ll try the card. If it won’t link at 25G, I can get a different one. Any recommendations? :)
Personnaly I'll probably go with some cheap mellanox card on ebay :)