Best Way to Communicate Data Between Two Identical Logix PLCs

Nah, you've got the gist of it.

PLC1(Lan1) would have its gateway address set to the private side IP of the NAT device(NAT1) it is connected too. It would setup produced consumed tags with PLC2(Lan2) using the Public IP of PLC2 according to NAT2).

Vice versa for PLC2.

You would need 2 NAT capable 'things' and a way to connect the 2 NAT things. The public side IPs of the NAT devices should be on a subnet that can talk to either public side range.

Dravik & drbitboy, please accept my gratitude for sticking with me as I try to understand this. I guess the part that I'm hung up on (and if you can try to explain this to me I'd really appreciate it), is I get that you can translate one of the PLCs to have a unique address such as 192.168.1.2 --> 10.10.10.2 as was shown in that Rockwell slide. What I'm having trouble with is how does that help the other side of the equation?

In other words, if I had a controller at 192.168.1.1 and an I/O node at 10.10.10.2, my understanding is they would not be able to communicate since they are on different subnets. What am I missing here?

Again, forgive my stupidity. I feel like this is super simple but I'm just not getting it.
 
Dravik & drbitboy, please accept my gratitude for sticking with me as I try to understand this. I guess the part that I'm hung up on (and if you can try to explain this to me I'd really appreciate it), is I get that you can translate one of the PLCs to have a unique address such as 192.168.1.2 --> 10.10.10.2 as was shown in that Rockwell slide. What I'm having trouble with is how does that help the other side of the equation?

In other words, if I had a controller at 192.168.1.1 and an I/O node at 10.10.10.2, my understanding is they would not be able to communicate since they are on different subnets. What am I missing here?

Again, forgive my stupidity. I feel like this is super simple but I'm just not getting it.

Maximuse -

That's where the 'gateway' part comes in.
The gateway address acts as a 'helper' that allows routing outside just the existing subnet.

Each NAT 'thingie' acts as a gateway for the private devices and allows them to communicate to the public IP range.

Essentially, PLC1 when asked to talk to something 10.x, which is outside its subnet range, will ask the gateway device to help it get there.
 
Sorry if i'm oversimplifying, but i've been up since 4am and am slightly loopy at this point. (I am NOT a morning person)
 
In other words, if I had a controller at 192.168.1.1 and an I/O node at 10.10.10.2, my understanding is they would not be able to communicate since they are on different subnets. What am I missing here?


Normally E/IP connections cannot make it through routers i.e. onto separate subnets. But with a proper amount of whatever-fu, it can work. I am pretty sure that is the point of that PDF, and the hardware it is hawking.
 
caveats -
You'll have to be using Unicast communications, Multicast is going to be a whole different can o' pain to get working.

If you use 1to1 NAT devices, You shouldn't need to muck w/ port forwarding.
If you use 1 to many NAT, Then you'll have to do port forwarding or stick the PLCs in the DMZ.
 
Maximuse -

That's where the 'gateway' part comes in.
The gateway address acts as a 'helper' that allows routing outside just the existing subnet.

Each NAT 'thingie' acts as a gateway for the private devices and allows them to communicate to the public IP range.

Essentially, PLC1 when asked to talk to something 10.x, which is outside its subnet range, will ask the gateway device to help it get there.

Thank you! That's the part I was missing. I was confused at how PLC A could see all of its 192.168.1.x connections AND all of the 10.10.10.x connections at the same time. Very good explanation and my apologies for not getting it. For most of my career I've been programming "isolated" cells for larger customers. Once it hits their floor their controls/IT handle integration into the broader network. Still lots to learn! 🍻
 
Sure -

Some NAT devices assign both a public IP and a private IP to each device - 1 to 1.

Routers - Like you might have at home, also do NAT, but usually default to 1 to Many. 1 public IP to many private IPs. This is where you might have to do fun things with port forwarding.
 
maybe it would be easier to stick a new 1756-enbt in one of the racks and do the produced and consumed between racks like that.
 
1 to Many.....

Think of your home Wifi router. You have one public IP address connecting you to the internet and many private IP addresses for all the device on your LAN. The router is performing the NAT function for every device on your home network.

OG

EDIT: Dravik already used this analogy. Oops.
 
Originally posted by diat150:

maybe it would be easier to stick a new 1756-enbt in one of the racks and do the produced and consumed between racks like that.

That would definitely be easier. It just depends on what each of us considers our time worth or if we want to learn something new along the way. I could get both NATRs that would be needed from my Rockwell distributor for a couple hundred less than ONE 1756-ENBT.

Keith
 
1 to Many.....

Think of your home Wifi router. You have one public IP address connecting you to the internet and many private IP addresses for all the device on your LAN. The router is performing the NAT function for every device on your home network.

OG

EDIT: Dravik already used this analogy. Oops.

Great minds and all :)
 
Im sorry I do not have anything to add, I just wanted everyone to know this Thread has been a great read and I have learned alot.

Thanks to all great minds out there.

Vinnie
 
In addition to doing NAT and Routing and or VLAN's if you wanted to keep it simple you could add a chassis with 2 ENBT or similar and connect 1 ENBT to each cell LAN and there would be no need to do routing or NAT or change IP addresses.

You could add a small/old processor in the chassis to do something with both values such as send them to an HMI or Message them to another system, etc.

You may have these items lying around or pick them up on eBay very cheap.

This is called a data concentrator. I could have 10 ENBT cars all with the IP address 192.168.10.30 connecting to cells A, B, C, D, and so on with all the IP addresses in each cell being the same and have no issues.

I have worked with many customers that prefer this method because it's something the maintenance and engineering team can do and when using routers and setting up NAT's in some plants has to involve IT and sometimes that doesn't go well depending on the plant/business culture and history.
 

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