hello, I have a server that has 10GB NIC and a switch with 1GB SFP ports can I buy a 10GB DAC cable at the 2 ends that will work? including the switch that is 1GB? Or can I buy an LC-LC cable and a QSFP+ connector to connect to the server and an SFP connector to connect to the switch?
The definition for DACs wasn’t introduced until the SFP+ specification, so not all SFP switches will work with them - on the other hand anything designed after SFP+ came out has a high likelihood of it working. BUT - you will have to manually set the port speed to 1Gb on the SFP+ end, because any “auto” setting just means to match the module, there is no negotiation with the other end, and all DACs will be auto detected as 10Gb.
If you want to use fiber, you would want an SFP module at both ends - otherwise the frequency and modulation between the modules would not match up. In this case the SFP+ port can be left at auto speed because it will recognize the SFP module as 1Gb.