The latest generation of PLCs have an integrated Ethernet port on the controller for two main operations. The first is controlling remote I/O on Ethernet based protocols like EtherNet/IP, Profinet, or Modbus/TCP (UDP) to name a few. The second is to program and/or debug the internal program of the controller. With these features, and utilizing the Ethernet’s other services such as a web and ftp server, remote administration of a control process becomes possible.
The first step in connecting remotely is to setup the controller to handle communication from both the local network as well as, handle messages from a wider network such as the Internet. This is accomplished by adding a gateway address to the Ethernet communication settings on the controller. Thereby, allowing the controller to send and receive IP messages that are not established inside the local network.
This gateway address is usually assigned to an Ethernet router. Routers provide a way of directing, or “routing,” IP traffic to the correct Ethernet device inside the LAN (Local Area Network). Routers come in all shapes and sizes; from a computer (with two NIC cards and routing software) to an off-the-shelf broadband router, both handle the communication traffic pretty much the same way. The most common way of routing network traffic between a LAN and wide area network (WAN) is to use a network address translation (NAT). NAT provides a way of taking a single IP address, supplied by the Internet service provider (ISP), and allowing multiple devices to share the same Internet connection.