CompactLogix CIP MSG Read via NAT 1:1

[celichi]

Hello Everyone,

Can two PLCs on two different subnets pass data via CIP MSG Read Instructions?

I would be using the HMS Fl3xy NAT 1:1 feature to route the traffic between the two subnets.

Thank you in advance.

 

[JeremyM]

If the networks have a route established, CIP packets are routable to other networks.

NAT is not routing.

 

[Ken Roach]

I don't think we need to discuss that "NAT is not routing": functionally NAT will forward most or all traffic addressed to a specific IP address on one side to a different IP address on the other, and do the same with the replies.

I say "most or all" because you typically have to set up the TCP Ports you want to include or exclude. TCP Port 44818 is used by a CompactLogix MSG instruction.

While multicast or unicast Produced/Consumed traffic would probably not work through an ordinary NAT interface, MSG instructions between controllers almost certainly will.

 

[celichi]

Thank you for the replies, I understand that "NAT 1:1" is not "Routing". Terminology is everything, and I appreciate that.

With NAT 1:1 enabled, I can "see" the private PLC (192.168.53.100) from the public subnet (192.168.153.xxx).

What I am struggling with, is how do I access the public PLC (192.168.153.200), from the private subnet (192.168.53.xxx) via the Flexy.

How do I get the communications to be 2 way?

 

[JeremyM]

You have to build a static route between subnets (static route settings in your image).

- Destination is 192.168.153.0 subnet.
- Mask is 255.255.255.0 (usually, but yours may differ)
- Gateway is the address of the private gateway (192.168.53.1, usually)

Both gateways need to exist.
Both PLCs will need gateway addresses assigned for their respective subnet.

 

[celichi]

Thanks JeremyM.

I also have a Proxy Configuration...would this be better than the other Static Route Table?

 

[celichi]

My preference is for each PLC to perform a CIP MSG Read, this way if you search for the address in the local PLC, it will take you to the MSG read instruction, and therefore the programmer can easily see where the data is coming from.

I was able to perform CIP Read and Write from Public PLC (192.168.153.200) to Private PLC (192.168.53.100) with NAT 1:1. by using the Public NAT address in the MSG write instruction of 192.168.153.100.

It would be "nice" to be able to perform a CIP msg read in private PLC reading public PLC tags, but not the end of the world if I can not.

I have options, I could change all the skidded devices IP addresses to match customer's mfg network, or just tell them to perform the read and WRITE to my PLC.