1783-NATR to with CompactLogix L32E

Ken Roach

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A new member of our Forum community, maheshbhaiya, posted this as PMs and a resurrected thread, so I'm going to give it a push in the right direction and post it to the main forum (lightly edited for formatting).

I am using 1783-NATR with L32E CPU.
CPU has IP address of 192.168.0.149, subnet 255.255.255.0. CPU is in private network.
My NATR module private network IP address is 192.168.0.152, subnet 255.255.255.0.
The public network IP address is 172.25.70.107 and subnet is 255.255.248.0.
On public network side my L32E CPU is mapped with IP address of 172.25.70.108 in the network address translation rules.
But still my PLC could not respond to PING on the public side. IP address of NATR module responds to PING on public side.
So please give me solution.

My first suggestion is to check the 1769-L32E's Default Gateway address. This needs to be the Local Network address of the 1783-NATR, so that the CompactLogix knows how to respond to messages that have been forwarded by a router device.

It is very common to leave that blank or set it for a common address like 192.168.0.1, which allows the PLC to be accessed on the internal network (where the Default Gateway is not relevant) but not via the router or NAT device.
 
Route Causes..

Hi Ken,

I read your post the other day and thought, good on you. Even if our friend dissapears, it's always good to "NAT" these "Private" requests out to the wider "Public" so as to discuss and try resolve these issues in a manner beneficial to the many, rather than the few.

I also felt today, as there had been no replies yet, that I would not only commend your efforts but also try to add to them, a little...

I would 100% agree with your first suggestion, Ken. And also that it's the most likely cause and solution here. Not setting the Default Gateway appropriately, when configuring Private NAT devices, or even non NAT devices, is a very common oversight when a router appliance is involved.

But also, and just to add another option for the future...

If a Private NAT device's Default Gateway is set correctly, then another common reason the PING utility might not work is that another enabled network interface on the workstation computer may be interfering with the command reply. That is, the PING command request is sent out the correct interface but the reply may be incorrectly serviced on the other, offending interface. Disabling said interface will usually resolve this issue (Example: Wireless or other NIC).

The reason I'm only suggesting this cause and solution, for the future, is because the...

maheshbhaiya said:
...IP address of NATR module responds to PING on public side...

...which tells us that the PING utility is working, in general, as the 1783-NATR is reachable from the user's workstation. So another interface would not likely be the cause, in this case.

This case definitely points to a routing issue beyond the NAT appliance on the Private side.

Regards,
George
 

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