NAT Application

Ewon Support eWON Cosy
#1

Good day support team. I have an application where a client desires to have two AB PLC’s to have the same IP address on the same LAN along with two HMI’s with
the same IP address on the same LAN to be reachable from the RTU which is on the same LAN. See below description and attached block diagram for how this is structured. The reason for the duplicate IP’s is coming from the end customer maintenance department
so if they need to replace a PLC or HMI they do not have to modify IP addresses on shelf spares. Is there an HMS device or gateway which could work for this application and if so where would we need to place them in the current configuration. Thank you in
advance.

“ The IP addresses in the diagram was the intended design (i.e. the dual-bridge’s PLCs needed to have separate IP addresses). However, the client wants to
use the same IP address for both PLCs. My hope is that we can use the Anybus X Gateway with NAT to allow both PLCs to work simultaneously without crashing.

I am assuming the Magellis HMIs will have same IP address as each other and would also need to utilize the Anybus X gateway w/ NAT. Note, however, we are not pulling data from the HMIs but from the Flex Logix PLCs. Please give me options
for both scenarios (i.e. the HMIs have same versus different IPs). Thanks a lot.”

Regards

#4

Hi Bob,

With the devices having the same IP address on the same network there is not a way of distinguish the difference between the devices with the same IP and this will cause a network clash.

#6

Hi Zach, thank you. Indeed this is why we were considering the Cosy 131 with NAT 1:1 so the two devices can have the same IP address on one side of the Cosy and
map them to unique different IP’s on the controls network side of the Cosy. This should work correct?

Regards

#9

So will you have two separate cosy’s connected to 2 different networks that have the same subnet? The problem with having two devices with the same ip connect to a single cosy is it will not be able to differentiate the two devices. The NAT 1:1 feature on the Cosy uses layer 3 so it will only be looking at the IP addresses and not the MAC addresses of the devices. The NAT feature also is for moving a device from one network to another so the devices will be in a different subnet. If you have it set this way the devices will need to have unique IP addresses after begin NATed to the WAN side.

#10

Hi Zach, my original email had a diagram of the network layout showing where the two AB PLC’s and Magelis HMI’s were located. The key
is the RTU in the middle needs to communicate to both PLC’s and HMI’s. The client wants each PLC to have its IP set to be the same and also each HMI to have their IP’s set to the same for purposes of shelf emergency replacements being preconfigured and drop
in ready for either location.

Regards,

Bob

#12

Hi Bob,

With the way the diagram is setup NAT would not work. The ewon requires to separate subnets to NAT the LAN to WAN. Since your RTU is in the same subnet there is no network that can be NATed to. If the RTU was on a different subnet then you could NAT, but then you would run into the problem of multiply devices with the same subnet on the ewon LAN side which would cause a clashes and would not be able to NAT the device since it is layer 3 and cannot tell the difference between the 2 devices.

#13

Thanks Zach, I’m going to need to review this with the client again.

Bob