Short version: Can't get an SFP28 DAC to work between sfp28-2 and an Ubiquiti switch, just no link lights up at any time and after trying many things I'm looking for ways I could further debug this to find what's wrong.
Long version: I have a CCR2004-1G-12S+2XS that has 25 gigs coming in on sfp28-1 and I would like to connect it on sfp28-2 to my network. On the Switch side, I have a USW-Pro-Aggregation from Ubiquiti. The switch then is connected to a server by a SFP28 DAC. The server has an intel card and the cable is a "LENOVO DCG 3m Passive 25G SFP28 DAC Cable" with a part number of 7Z57A03558 according to my online shop of choice. I also tried a cable form Ubiquiti, namely the UACC-DAC-SFP28-3M one.
Now the Lenovo cable works between switch and server. Unplugging it from the server and plugging it into the router does not work. I tried another Lenovo (probably, though not 100% certain that it's the same) DAC and that one didn't work either. Then I tried the Ubiquiti cable and the same state, no blinking lights, or at least static light up to see a link was established. I did try all 4 ports on the switch with the server, they all seem to operate just fine. Then I tried the ports with all three cables, and the router, and no go.
I do have a 1G sfp module in the router that connects to one on the switch at the moment, merely to have some kind of connection going and of course I removed that on both sides just to be sure, before any testing to not create a loop. There is nothing else plugged into the router, just line in, and then out only over the 1g module, or only the second sfp28 port when testing.
During testing I tried setting values on both sides by disabling auto negotation, setting the ports speed manually, enabling, disabling flow control, etc. Nothing worked.
I have not seen any errors or warnings or anything else pop up anywhere on both sides. My conclusion is I'm missing something somewhere, as in I'm not looking in the right place or not running the right commands to get more debugging output. Searching for this problem has sent me to tons of places where I can buy DAC cables or the Mikrotik router, so far none where I would be able to read up on how to debug this better.
Any pointers to where I might find more help are greatly appreciated