Compact Logix 5343 1768-L43 Communication Issue

[chrisreisinger79]

I have a question concerning network connectivity to a Compact Logix 5343 1768-L43 processor.

Some background information:


1) The 1768 PLC
a. IP Address is 192.168.1.16
b. Subnet Mask is 255.255.0.0
c. Gateway is 192.168.1.100


2) There is a touchscreen Windows computer that is an operator interface and communicates with the 1768 PLC
a. IP Address is 192.168.1.100
b. Subnet Mask is 255.255.255.0
c. Gateway is BLANK

3) Both of these are routed through a Allen-Bradley Stratix 6000 (1783-EMS08T) Managed Ethernet Switch

4) Currently this PLC is not connected to our local network. Our local network addressing scheme is as follows:
a. IP Addresses are 10.0.228.xxx
b. Subnet Mask is 255.255.254.0
c. Gateway is 10.0.228.1

5) I am working on a project that requires this PLC to be added to our network in order to communicate with another PLC. In order to accomplish this, it was suggested by one of our corporate techs to use an Allen-Bradley NAT Router (9300-ENA). I programmed it as follows:
a. Uplink Interface (Public)
i. IP Address: 10.0.228.18
ii. Subnet Mask: 255.255.254.0
iii. Gateway: 10.0.228.1

b. Local Interface (Private)
i. IP Address: 192.168.1.100 (per the explicit directions of the 9300-ENA this needs to match the Gateway of the 1768-PLC)
ii. Subnet Mask: 255.255.254.0

The communication was successful and I was able to get online with 1768-PLC. However, I ran into a problem. The touchscreen Windows computer lost its connectivity to the 1768-PLC with an IP address conflict. Because its IP address (192.168.1.100) matches the Local Interface IP address of the 9300-ENA, there is a conflict with two devices having the same IP address. I am guessing that the touchscreen Windows computer IP address has to match the Gateway of the 1768 PLC in order to communicate with it just as the 9300-ENA has to.

Do anyone know if there is any way to program either the 9300-ENA or the Stratix 6000 to accomplish having the 1768-PLC on our network or is there another device that can accomplish this while still preserving the connectivity of the touchscreen Windows computer?

 

[drbitboy]

There cannot be two nodes on the 192.168.0.0/16 (=192.168.x.y/255.255.0.0) network with the same IP address, but the configuration described has two nodes with the same IP address 192.168.1.100: the Windows computer; the 9300 ENA local gateway.



The gateway address for the 1768-L43 and the IP address of the LAN side (i.e. the gateway) of the 9300 ENA need to be the same.


Either

• the IP address of the Windows computer needs to change (it is not a gateway),
• OR
• two values,
  • need to change:
    • the gateway address (not the IP address) configured on the 1768-L43, and
    • the LAN side of the 9300 ENA,
  • and those two values need to be the same value e.g. 192.168.1.101.

Also, in item 3) it says the PLC and Windows are "routed" through a Stratix 6000 - I think that should be "connected" because the 6000 is a managed switch, not a router.


Part of what may be confusing is that the system was working when the gateway address of the 1768-L43 was the same as the IP address of the Windows computer, which was an incorrect configuration. However, since the 1768-L43 and the Windows computer did not communicate with any other networks, it did not matter that the gateway setup was mis-configured; in fact, it would have worked even the the 1768-L43 has no gateway address configured at all, similar to the Windows computer.



There are many explanations of routing and NAT on the internet, I suggest reading them so informed choices can be made for configuration values in the future. Here is my attempt to explain routing and NAT: https://github.com/drbitboy/nat.

 

[Dravik]

As a note, since I work on both ends(IT and Automation), This is a classic example of making sure that ALL information is provided in both directions.

Points 1-5 as you noted contained enough information to identify an issue and give you back better more specific guidance from your Corporate techs.

Assumptions always bite us in the end.

 

[chrisreisinger79]

Thanks for the help everyone. I am hoping to try this during our late afternoon shutdown today.