Blog post by Project Engineer Sean Callaghan

As with most aspects of life, when working on a control system one of the vital components for success is communication.  Whether it is between the PLC, HMI, server, or even your own personal computer when communication breaks down, everything comes to a halt.  Communication errors can be confusing to solve.  This article will illustrate how to identify what part of the system needs attention in order to correct the issue.  Within this post we will be focusing on IPv4 connections.

The first step one may think is to verify that everything is physically connected.  While considering loose or faulty wires is an intuitive thought processes, within a facility, campus or potentially even large network between sites, the time it would take to reach each individual point verifying connection could take hours.  Using software tools to aid in finding which specific device to look at will allow you to narrow the search.  This saves time when repairing the problem, allowing you to remotely fix the connection or go directly to the impacted device.

Within these instructions, the main interface used will be the Command Prompt.  The Command Prompt is a tool used to provide commands directly to your computer by typing in specific commands and pressing enter to execute them.  Opening the Command Prompt is similar to opening any other program and can be done through the start menu by searching for CMD or using the run program and entering “cmd.”    Doing so will open up a terminal which we will use for troubleshooting.

Ping

The first step in evaluating connection problems is to verify that the problem is the connection and not related to the software tool being used.  Due to its simplicity and speed, the best tool for quick connection tests is the ping command.  The ping command sends data packets from your computer to a target location on a network and provides you feedback on whether or not the connection was successful. It is similar to sending four letters by certified mail and either getting four receipts or the letters back indicating a failure to deliver. However, unlike the postal service, the ping command will complete within a matter of seconds.

To use the ping command within the Command Prompt, type ping followed by the target device’s IP addresses, device name, or local name and press enter to execute the command.  For example, if you wanted to test your connection to google.com you would enter ping google.com and press enter.  Pinging will then send four packets of data to Google and should return four replies if you are connected to an Internet connection which can reach Google.

Additionally, if you wish to reach a device within your network with an IP address of 192.168.10.73, you would type ping 192.168.10.73 as a command to test the connection.  A successful ping will show a reply from total bytes, time, and TTL (time to live) as well as all packets received.  If the ping is successful but there are still connection issues, then there may be port configuration issues which will be covered in another article.  An unsuccessful ping can present in multiple ways but will show either packets lost or the destination host was unreachable.  Examples of both can be found in the quick reference guide below.

With an unsuccessful ping, the next check would be your adaptor settings to verify your Internet configurations. Checking settings can be done either through the control panel or with the ipconfig command using the command prompt.  Verifying the communication settings can be thought of as sending the letters mentioned earlier with the correct postal service to ensure they get to their proper destinations.

Ipconfig

Within the Command Prompt entering in ipconfig will show you information of each adaptor’s IP configuration.  This allows you to quickly verify settings such as IP address, subnet masks, and selected gateways for each connection.  Changes to an adaptor can be made either in the control panel or through entering the code below in the Command Prompt replacing the bracketed terms with each specific case.

netsh interface ipv4 set address name=”[Adaptor Name]” static [IP Address] [Subnet Mask] [Gateway]

Within the control panel, select the “Network and Internet” option which will display your current active connections.  If no network connection is displayed for the target network, you will need to connect with either a connection cable or wirelessly.  Once connected, select the specific connection you are using to reach the target device.  The status screen will open from which you will want to select properties and then “Internet Protocol Version 4 (TCP/IPv4)” to open the adaptor properties.

Normally a computer will automatically obtain an IP address assigned by the network.  If the device you are connecting to is on a specific subnet, select the “Use the following IP address” option and enter an unused IP address within that network to connect or enter the correct a gateway address to allow cross-network traffic.  Attempt to ping the target to verify a good connection.

If the network settings are correct on both devices and the ping command fails, then potentially there is an error within the network devices being used to pass the data between the two devices.  Within large networks, each device used must be correctly configured to pass the data between themselves without corrupting or blocking the flow.  To verify the pathway and trace the route of the packets, we can utilize the tracert command.

Tracert

Similar to a chain of custody for important packages, tracert checks each intermediate step the packets take while moving through the network.  The tracert command is used similar to the ping command by entering tracert followed by the target address.  The output lists each device and connection the data passes through while the trace is active, and ends with “trace complete.”  If the trace completes prior to reaching the target, the last device shown is where the trace stopped.  If the trace stops at a device, look for errors in its configuration to solve the network issue.  If a trace successfully reaches the target, then you should be able to ping the device and communicate without issue.

While all these commands can be used to quickly and effectively test your network connections in under a minute, they are just a few of the tools in the belt of troubleshooting.  Port configuration, loose connections, and countless other potential issues all represent possible points of failure. By taking a minute to run these commands, your response can be better targeted and more efficient allowing you to be operational more quickly.

Click to download a quick reference guide for using the commands listed in this post.Quick Tips for network troubleshooting-preview

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