PCIe 2.0 cards (such as ConnectX 3) are $30 used on ebay.
The modern versions (ie: ConnectX 6) are much more expensive of course, but the older hardware might do better with FreeBSD / Linux anyway. Of course, your mileage may vary so do some research before buying (or buy for $30 and hope for the best).
You'll also either want Optical Transceivers + Fiber, or Active Fiber (aka: Fiber that has transceivers soldered onto them already), or DAC (direct-attach copper, the cheapest but only works over small distances).
Optical Transceivers + Fiber is the most flexible of course, different transceivers are spec'd for different wires and different costs though, so it gets a bit complicated.
Active Fiber and DACs are is probably easiest, but if you buy a 10m cable but need like 12m, you need to buy a new cable + transceiver combo (rather than just purchasing a bunch of different fiber lengths).
Length and cost is the big difference from Active Fiber and DAC, but otherwise are very similar in use. You plug the modules into the SFP+ port, hope its compatible and let them rip.
ConnectX3 and Intel SFP cards are pretty reliable and easy enough to get working on Linux. On my Windows 10 Pro machine, all the cards I plugged in just worked immediately, no driver install required.
I'd start there and if you find you need other features, think about spending more.
My ConnectX-3 on Windows 10/11 machine takes 15 secs to reconnect on resume from sleep. It's not serious issue but a bit annoying. Anyone had similar issue?
The modern versions (ie: ConnectX 6) are much more expensive of course, but the older hardware might do better with FreeBSD / Linux anyway. Of course, your mileage may vary so do some research before buying (or buy for $30 and hope for the best).
You'll also either want Optical Transceivers + Fiber, or Active Fiber (aka: Fiber that has transceivers soldered onto them already), or DAC (direct-attach copper, the cheapest but only works over small distances).
Optical Transceivers + Fiber is the most flexible of course, different transceivers are spec'd for different wires and different costs though, so it gets a bit complicated.
Active Fiber and DACs are is probably easiest, but if you buy a 10m cable but need like 12m, you need to buy a new cable + transceiver combo (rather than just purchasing a bunch of different fiber lengths).
Length and cost is the big difference from Active Fiber and DAC, but otherwise are very similar in use. You plug the modules into the SFP+ port, hope its compatible and let them rip.