Normal "external HDD's" cannot connect directly to a network because they have no "smarts" for network communications. The units that do that are usually called Network Attached Storage (NAS) devices. They often do NOT have USB2, eSATA, etc. connectors on them, because those would be redundant (and add cost) because you already have a way to connect via a network. Even if you find yourself in a situation with no router, etc., and only a stand-alone computer to connect to, almost always the computer will have a LAN port and can be set to use a network. So you can just plug the NAS unit directly into the computer's LAN port and set up a "network" of 2 devices.