Comment by Terr_

I still keep an old 4-port hub in my junk-box because that way I can diagnose/snoop on network traffic... Although so much of it is encrypted these days that it's harder to see what's going on.

P.S.: Yes, modern alternatives would be to to buy a switch and that can be configured to "mirror" packets onto a chosen port, or a smalls Ethernet network tap unit... But why buy more stuff if I don't really need to?