RJ-45 is the 8-conductor Version of an RJ-11. It looks like a regular modular phone connector, only it's wider. You need to use RJ-45 for Ethernet, because the connection standard puts the Ethernet on some of the outer connectors not in RJ-11. RJ-11 plugs will fit into an RJ-45 socket, but because the plastic plug is smaller, some of the contacts will get bend back a little more.