Pepperl+Fuchs Blog

I Lost My IP Address!

Posted by Tim Cicerchi on Thu, May 23, 2013

The IP address is a critical part of the network for industrial Ethernet devices

This may sound ridiculous. Most of us have experience with commercial Ethernet devices such as PCs, DSL modems, network printers, etc. All of these devices set their IP addresses automatically using a network DHCP server. The PC or printer name is all that is important.

Find that lost IP address
Industrial Ethernet products work on factory floor networks where device names are not used. The IP address is a critical part of the network infrastructure. The PC or PLC doing the communication knows the IP address of all the devices on the network. If you install a new device in the field, the IP address must be set first. Unlike your normal everyday PC, you can’t log into an Ethernet barcode reader with a monitor, keyboard, and mouse and simply reconfigure the device. The IP address needs to be reconfigured by other means.

That being said, have you ever been in a situation where an industrial device’s IP address was changed from the default and you forgot what you set it to? It’s happened to me. After talking to a customer, I sent out a barcode reader with the customer’s specific IP address requirements. A few months later when I got the demo back, I couldn’t connect to it. A light bulb went off in my head that I had changed the IP address, but what did I change it to? I had to find another way to talk to that device or reset that device back to the defaults.  

It took a little extra work to figure out the IP address but I finally got it. I decided maybe it would be a good idea to look into my other Ethernet devices and see how easy it would be to get the IP addresses of those devices if they were ever forgotten. You have to realize that industrial devices, often as a cost-saving measure, may not have good external means of setting the IP address. Here are some different ways I found to set the IP address.

Rotary Switches

The IdentControl Compact RFID system has a rotary switch located on the bottom of the module. One of the rotary switch options is to set the IP address back to known default. After you power cycle this RFID control, a PC can easily log into the device’s web interface and change the IP address to the correct one.

Graphical Display

Some devices, including our AS-Interface Ethernet gateways and our RFID four-channel controllers, have graphical displays. If a device has a graphical display, using the display is always the preferred method of resetting or changing the IP address settings. Whenever a graphical display is available it typically is always used. If you don’t need a PC to reconfigure a device, then why use one?

ARP Messages

The address resolution protocol (ARP) is normally used for switches, PCs, and devices to resolve the MAC address to the IP address. I found that many of our devices send this message out one time on powerup. These devices include:

  • TCP/IP encoders
  • IDENTControl Compact RFID controllers
  • IDENTControl four-channel RFID controllers
  • BIS510 sheet verification sensors
  • OIT500 high-temperature ID system
  • VDM100 precision distance measurement sensor.
I noticed that our BIS510 vision sensorrequires a switch to be located between the PC and the sensor for this to work, however, and this may be the case for your devices as well.

You can see ARP messages using a program called Wireshark. This is a free downloadable program that allows you to see every Ethernet message entering or leaving your computer. Be aware that there can be a lot of traffic. I found it easiest when you have only one computer and one device on your network. This way, you know exactly which two devices are communicating with one another. Keep in mind that a lot of companies don’t allow Wireshark on the main network for fear that it will allow you to read other people’s emails or see confidential information. These fears are typically unfounded because most Ethernet switches are not going to send you other people’s personal emails anyway. But get permission from your IT department before using it or take your network components off the main network.

Wireshark capture screen showing an ARP messagePicture 1This is a Wireshark capture screen showing an ARP message with IP address being sent to your computer

Picture 1 shows an ARP message being sent to your PC. When you see the proper ARP message, you can ping that device to double-check that you can communicate with it. As I said, it is easier with only two devices on the Ethernet network; your PC and the Ethernet device for which you are trying to find the IP address. In this case, there can be only one device sending an ARP message … besides your PC, that is.

LLDP messages

Some devices don’t send any ARP messages. Many at regular intervals will send a Link Layer Discovery Protocol (LLDP) packet. This protocol allows devices to learn where other devices are on the network and how they are configured. Fortunately, this message also includes the IP address information. You can analyze this message using Wireshark.

Wireshark capture screen showing a LLDP messagePicture 2: This is a Wireshark capture screen showing a LLDP message with IP address being sent to your computer

Once you find an LLDP message, you will have to drill down a little bit to see what the IP address is. See Picture 2. Many of our devices use this protocol including:

  • EtherNet/IP encoders
  • PROFINET encoders
  • All RFID controllers
These LLDP protocol messages are generated by these devices because they all support PROFINET. There are other ways to set the IP addresses as well. See Primary Setup Tool.

Primary Setup Tool

The IP addresses of PROFINET devices can easily be set without knowing what the IP address currently is.  The reason is because the LLDP messages, which are sent all the time, are easily interpreted by PROFINET software. Siemens offers a free tool called Primary Setup Tool. This is a very nice software tool for assigning IP addresses as well as performing PROFINET name changes. Certain devices such as RFID controllers can use this tool only when using PROFINET. Once you start talking EtherNet/IP or another protocol besides PROFINET, this tool typically can no longer be used. The simple reason is that the other protocol stacks like Modbus/TCP or EtherNet/IP, which you may be using, don’t require LLDP communication.

Secondary Port Connections

Some of our devices can have the IP addresses changed if a secondary serial RS232 connection is made. The MAC502 barcode imagers and the WCS EtherNet/IP couplers have this capability. Make sure you have the right cables and RS232 to USB converters, if required, to perform this task. You’ll notice that a lot of new computers don’t have RS232 ports so nowadays a converter is a must. Also these devices won’t just have SUBD RS232 ports on them. A special cable is usually required and sold by the industrial Ethernet device manufacturer.

Barcode Setup

Some of our optical devices can read a special barcode on powerup. This barcode resets the internal parameters to known defaults. The OIT500 high-temperature identification system and the PCV Data Matrix Positioning System both have this capability. This option only really makes sense if the product is down on the work bench. If one of these devices is on an overhead conveyor 20 ft. off the ground, using this barcode setup is possible but not practical.


You can see from my list of IP address setup options that many devices have multiple ways to reset the IP address. I have not found a device yet where the network parameters cannot be recovered and then changed. There are many different ways to do this and you have to figure out which one is easiest for you. Try the easier reconfiguration options first and if you still have trouble move on to Wireshark. Always double-check that the device can’t be communicated with using the standard default settings. I would hate to have you go through all this work just to find out that the Ethernet parameters were never changed in the first place. If you need help reconfiguring any Pepperl+Fuchs device, give us a call or use our Ask an Expert form. We are glad to help. If the device isn’t ours, call the manufacturer for assistance.

Need help with a lost IP address? Ask an Expert!

Topics: Troubleshooting, AS-Interface, RFID, Software

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