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I have a PLC that has a hardcoded IP of 10.100.30.130 that I would like to access on our LAN.

I can ping it now only if I plug it directly into my computer and change my computer IP to a 10.100.30.xxx address but I can't always be changing back and forth.

Would it be possible to add a second NIC card or use a USB to ethernet adapter to have 2 separate networks configured on my computer? Or is there a way to get this to work in our router? We have a Watchguard XTM router and windows server2012 with DHCP.

I have looked into using a NAT of some kind but got lost pretty quick and don't even know if it is possible. Any input would be much appreciated!

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    If you have a windows PC, just go to the Advanced tab on the IPv4 properties of your Local Area Connection, you can add in secondary networks there.
    – NickW
    Mar 26, 2014 at 14:54
  • You should be able to add a secondary network on the Watchguard for the PLC subnet. Add an unused ip address for the PLC subnet as a Secondary Network on the appropriate Watchguard interface. The Watchguard will then happily route traffic between both subnets. This is assuming that you can configure the DG on the PLC to be the ip address that you add to the Watchguard for the Secondary Network.
    – joeqwerty
    Mar 26, 2014 at 15:39
  • So if the PLC is behind the Trusted interface of the Watchguard then you would add a Secondary Network to the Trusted interface for the PLC subnet. Whatever ip address you use for the Trusted interface will be used as the Default Gateway address for the PLC.
    – joeqwerty
    Mar 26, 2014 at 15:41
  • @joeqwerty That should be an answer.
    – longneck
    Mar 26, 2014 at 18:56
  • You would probably want to implement a VLAN for the PLC network, to keep them separated.
    – Bert
    Mar 26, 2014 at 22:40

5 Answers 5

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Wondered what type of PLC it is, is it Allen-Bradley / Siemens or other?

You, should be able to set the subnet mask and gateway on the PLC as well ... unless you do not have access to check or change the subnet.

The last answer is also the best way to approach it ... the PLC network should, where possible, be on a separate subnet with only specific ip's and ports allowed through a router connected to the corporate, or local business network.

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  • I know this doesnt really answer my original question but it is what fixed the problem. The PLC was a Hydac eVision2 and we were able to change the IP address using the PUTTY terminal.
    – user214110
    May 2, 2014 at 18:40
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You can add secondary IP address (network) to your interface and it will work like a charm.

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You should be able to add a secondary network on the Watchguard for the PLC subnet. Add an unused ip address from the PLC subnet as a Secondary Network on the appropriate Watchguard interface. The Watchguard will then happily route traffic between both subnets. This is assuming that you can configure the DG on the PLC to be the ip address that you add to the Watchguard for the Secondary Network.

So if the PLC is behind the Trusted interface of the Watchguard then you would add a Secondary Network to the Trusted interface for the PLC subnet. Whatever ip address you use for the Secondary Network on the Trusted interface will be used as the Default Gateway address for the PLC.

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You can definitely have a secondary NIC, USB or otherwise, that is connected to the device. You can then configure that NIC to have an IP in the same range as your PLC.

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    +1 We use a second NIC all the time to do this easily. Works well and can also be handy "In the field" when working on a controls network.
    – Dave M
    Mar 26, 2014 at 16:35
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Another way you could do it, is give a small router an IP on your internal network (192.168.1.105, for example). Then plug the PLC in behind the router, and have a NAT rule and port forwarding send traffic to the actual PLC at 10.100.30.130

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