1783-NATR Public/Private Conflict

Maximuse

Member
M
Join Date
Apr 2013
Location
Ontario
Posts
51
Hello all,

I have two identical cells. Each have a PLC, HMI, Laser etc. The IPs are also identical so for instance both PLCs are 192.168.10.1. It would be ideal if they could stay that way.

I need to add a database PC that will be able to pull data from each of these PLCs. Can I add a NAT to one of the cells (Let's call it Cell A) and have Cell A on the "Public" side while Cell B is on the "Private" side without changing any of the device IPs?

Essentially I'm asking if the NAT will bark at me for having the same subnet on each side.

What I'm thinking is:

Cell A PLC IP 192.168.10.1 (on public side)
Cell B PLC IP 192.168.10.1 (on private side)
NAT Public IP 192.168.10.200
NAT Private IP 192.168.10.201
Translation 192.168.10.1 --> 192.168.10.10

So I'm hoping to end up with:

Cell A PLC IP 192.168.10.1
Cell B PLC IP 192.168.10.10

I'll be the first to admit I'm not great with subnets/network theory etc. I have a feeling this won't work. Can anyone confirm/deny?
 
Should work with 1:1 NAT mapping using 1783-NATR.

Worst case scenario, just create a public broadcast domain with different subnet and buy one more NAT device.
 
The NAT literally just arrived after I typed the first post so I've tried it now. No joy. After I finish inputting the Private and Public IPs of the NAT I reboot and the OK light changes to flashing red which from the pamphlet seems to indicate a duplicate IP address. This is with nothing else connected to either the Public or Private ports other than my laptop. Worse yet, I can no longer connect to the NAT to access the configuration. I ended up having to reset to factory defaults. Tried again, same problem.

I appreciate the suggestion about buying another NAT. Is there any other way to do this?
 
I put in several NAT devices in my facility on equipment that was competing for IP addresses. In your last update, you mentioned the IP conflict. Your public and Private networks can not be the same network. We ended up getting the IT department to give me a network that I could use as a PLC network. We used 172.xxx.xxx.xxx because the local IP address of my lines are 192.xxx.xxx.xxx. This allowed me to use the NAT device to connect my local 192 plc to my 172 public network. Food for thought, does your plc have two network ports on it, or do you have the space to put in another network card that can be used for public access?
 
The PLC is an AB 1769-L33ER. It does have two E/IP ports but obviously on the same network unless there's a way to configure them separately that I haven't come across.

Thanks for the reply. You've confirmed what I was worried about. Seems like I'm either going to have to:

1 - Buy another network card for one of the PLCs
2 - Buy another NAT
3 - Re-address the IPs on one of the cells
 
Maximuse said:
Hello all,

I have two identical cells. Each have a PLC, HMI, Laser etc. The IPs are also identical so for instance both PLCs are 192.168.10.1. It would be ideal if they could stay that way.

I need to add a database PC that will be able to pull data from each of these PLCs. Can I add a NAT to one of the cells (Let's call it Cell A) and have Cell A on the "Public" side while Cell B is on the "Private" side without changing any of the device IPs?

Essentially I'm asking if the NAT will bark at me for having the same subnet on each side.

What I'm thinking is:

Cell A PLC IP 192.168.10.1 (on public side)
Cell B PLC IP 192.168.10.1 (on private side)
NAT Public IP 192.168.10.200
NAT Private IP 192.168.10.201
Translation 192.168.10.1 --> 192.168.10.10

So I'm hoping to end up with:

Cell A PLC IP 192.168.10.1
Cell B PLC IP 192.168.10.10

I'll be the first to admit I'm not great with subnets/network theory etc. I have a feeling this won't work. Can anyone confirm/deny?
Click to expand...

If your intent is to have the same exact IP address, public and private, leave Cell A out of the NAT setup and connection. It will continue to be 192.168.10.1.

Set up Cell B on the NAT and now you have something to translate. Make sure that when toy assign the IP address to the private side that you set up the gateways correctly.
 
Something to keep in mind when doing all the configuration, is that you will need to change the default gateway on the PLCs and HMIs to the IP address of the NAT. Otherwise they will not communicate out to the public domain.
 
Cell A would stay on the public side with an IP of 192.168.10.1

1. Set up the NAT with a Public and Private IP address. Note: The private side IP address is the gateway on all translated devices
2. Create the translation 192.168.10.10 (Public)= 192.168.10.1 (private)

Now Cell B will be 192.168.10.10 on the public side.

Another thing to note. I have never tried using a NAT within the same IP range. I usually change at least the third octet. You might want to check the manual.
 

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