Allen Bradley PLC messaging accross Subnets

Hi All,

Our networks are a mess at our site and are going to be slowly fixedup. In the meantime I have a need for a Control Logix L71 to message to the controllers below. Im not sure how to get around the Subnet Issue. We are using a Cisco SG500-52 Switch.

Read/Write From
- Control Logix L71 - 128.146.30.40
To
- Micrologix 1400 - Ip 10.10.10.1
&
- Another Control Logix L71 - 192.168.10.1 (will use produced and consumed tags if possible)

Any Suggestions?

Not something I've personally done before but should be achievable once proper routing, gateways, etc. are all set up.

Configuring the correct subnets and gateways on the PLC's is relatively easy, however configuring the routing on the Cisco SG500 can be tricky.

Here's an example of what I would do assuming use of simple /24 subnet mask.
CLX L71 #1 - set subnet to 255.255.255.0 and gateway to 128.146.30.254
MLX 1400 - set subnet to 255.255.255.0 and gateway to 10.10.10.254
CLX L71 #2 - set subnet to 255.255.255.0 and gateway to 192.168.10.254

Now you will need to configure switch ports and routing on the Cisco SG500.

Connect CLX L71 #1 network to port 1 and set this ports IP address to 128.146.30.254
Connect MLX 1400 network to port 2 and set this ports IP address to 10.10.10.254
Connect CLX L71 #2 network to port 3 and set this ports IP address to 192.168.10.254

Now you need to configure static routes so any traffic looking for the 128.146.30.0 network goes to port 1, 10.10.10.0 network goes to port 2, and 192.168.10.0 network goes to port 3.

Note this is just an example of one way to set it up to give you an idea. Depending on existing network infrastructure and subnets it is most likely necessary to do it differently.

Agreed with the correct routing and managed switches it will work.

Are the current IP addresses currently being used for any external comms?
can they be changed to start aligning without breaking the process?
Once they are all in the same network segments the Cisco config will be easier.
Maybe a gateway PLC with a Network card for each network.

Hi Kellian,

The other L71 has quite a few other devices connected to it and would be too much downtime to change and test everything at this stage. However the Micrologix and associated equipment could be done without too much issue.