Connecting to the PLC from a Remote Location

Connecting to the PLC from a Remote Location


Industrial automation is no longer limited by the walls of a production floor. Increasingly, automation is handled through remote communication, whether from the office or from the comfort of your home. Today’s PLCs give you the ability to access your control system to handle tasks such as monitoring through a website to determine the condition of a machine or check other statistics. With the latest PLC technology, almost anything that can be accomplished at machine side can be accomplished wherever there is an internet connection.

connect to the plc from a remote location

Reading: How to connect plc to network

the latest generation of plc has an ethernet port built into the controller for two main operations. The first is to control 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 controller’s internal program. With these functions and using other ethernet services, such as a web and ftp server, remote administration of a control process becomes possible.

The first step in connecting remotely is to configure the driver to handle both local network communication and messages from a larger network, such as the Internet. this is accomplished by adding a gateway address to the ethernet communication settings on the controller. thus allowing the controller to send and receive ip messages that are not set within the local network.

This gateway address is usually assigned to an ethernet router. routers provide a way to direct, or “route”, ip traffic to the correct ethernet device within the lan (local area network). routers come in all shapes and sizes; From a computer (with two nic cards and routing software) to a commercial broadband router, both handle communication traffic in much the same way. The most common way to route network traffic between a LAN and a wide area network (WAN) is to use network address translation (NAT). nat provides a way to take a single ip address, provided by your internet service provider (isp), and allow multiple devices to share the same internet connection.

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Unfortunately, nat does not provide a true end-to-end connection. this means by default that a tcp connection established outside the local network will not be able to connect to the target device, because the ip address of the target device is hidden behind the router. For this type of communication to occur, the port forwarding process must be used. port forwarding occurs when communication from outside the network sends a message to the router’s ip address; the router determines where to send the packet based on the port number. the natural lack of end-to-end connectivity can be considered a problem in some circumstances, but it also provides a simple means of network protection.


By connecting a programmable logic controller to a network with internet access, the device will be exposed to the same potential security threats as a computer.

One of the best security measures is to select a driver that uses an embedded operating system that is not popularly used by the consuming public. this helps prevent the plc from being vulnerable to attackers using known vulnerabilities in the operating system because the knowledge base is much smaller. “security through obscurity” is the phrase coined for this type of security measure.

In addition, a properly configured router can provide effective protection for the control network from potential attacks. using the lack of end-to-end connectivity avoids most unsolicited requests for communication outside of the local area network. when configuring a router, be sure to limit the number of open ports. for example, an open ftp port can lead to a potential vulnerability when loading a program to override the driver. the best rule of thumb is to never keep a port open that is not used regularly.

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for added protection, a virtual private network (vpn) can be set up to increase security by encrypting data transmission when traveling over a public network, such as the internet. instead of opening all the ports needed to manage communication with the control network, a single authenticated network port passes encrypted communication so that the user can have all access as if they were inside the local area network.


By applying these simple techniques to modern control networks, new options are available for control design. data collection over long distances is one of the best uses of this technology. control systems can be more easily integrated within an enterprise network to couple supply chain management to the shop floor.

about the author paul reszka, applications engineer at wago corporation, tel: (262) 255-6333 ext. 154 or email: paul(dot)reszka(at)wago(dot)com. wago is a leading manufacturer and innovator of automation and control components with spring pressure connection technology, also known as cage clamp, which offers quick, easy and maintenance-free wiring. Its product range includes PLCs, IPCS, Fieldbus I/O, IP67 I/O, Terminal Blocks, Relays, Power Supplies, Interface Modules and more. For more information, visit

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