This is a small network with Comcast ISP ( Cable ), there are 11 PC connected to network all are wired Ethernet, the same 3 computers will loss there internet connection sometimes, not all at same time. the three can still access shard folders and the server based apps they run. I have replaced the switch( used to add ports for printers) and patch cables and same issue happens. I had a guy tell me it was like the ISP, so i called them and the tech did a diagnostic test, she got back on phone and said there was a downstream issue detected by the software. I am not sure what she is using.. then, the next day, the tech came out the next day and said, there is nothing wrong- the modem has a strong signal. What options are to determine the root cause, what can I consider. Could network cars be issue? I'm lost.