I recently purchased a CRS310-8G+2S+IN and wanted to connect it to a RB260GSP I already own through the SFP interface but can't find a way to do that. I tried some SFPs I have with some LC-LC cables and also two XS+DA0003 direct pigtails to no avail, everything is correctly detected by the two switches, but the link stays down. They do work as expected if I connect them through a traditional Ethernet cable, but using the SFP port would allow me to spare a valuable port per switch. This is my 1st experiment with optic links and SFPs in general so I could very much have missed something, but have no idea of where the problem could be.
Thanks in advance for any help.

Force the link speed to 1G on the CRS310 side.

Thanks, that was it. For the record, I also had to disable auto negotiation on the RB260GSP too.