Allen Bradley PLC Communication

Hi

This may seem trivial to some but I need to know the answer to my problem.

We have two separate network systems A and B

In system A all the IP address will be in the range of 192.168.1.xxx

In system B all the IP address will be in the range of 192.168.2.xxx

Now I want to send some messages between PLC in system A to and from PLC in system B.

With the network address configured as above is this possible? I tried to set my PC IP to 192.168.1.XXX and ping a PLC that's set to 192.168.2.XXX and I could not do it.

Can anyone help

They are not on the same subnet, I suspect.

It would work if you change all the subnet mask from 255.255.255.0 to 255.255.252.0 which would give you a host address of 192.168.0.0 to 192.168.3.255

The default subnet mask of 255.255.255.0 is limiting your "sub-network" for network A to 254 usable address of 192.168.1.0 through 192.168.1.255 (0 and 255 are not usable).

The default subnet mask of 255.255.255.0 is limiting your "sub-network" for network B to 254 usable address of 192.168.2.0 through 192.168.2.255 (0 and 255 are not usable).

So the devices on the two different networks cannot "see" each other. Most obviously on your PC, you cannot ping the other network. This can be resolved either by adding a router to route messages from one network to another, or by modifying the subnet mask for your devices.

A router can be a great item to help keep traffic on the two networks from bogging the network down. It can help isolate broadcast and multicast traffic. It can also add security to determine who can access which networks. But routers cost money, require setup, and can actually slow down the transfer of data from network A to network B.

As harryting suggested, modifying the subnet mask to 255.255.252.0 will allow a larger subnet (more ip addresses). It's a quick and easy fix. But now you have more devices talking on the same network. This can cause performance issues as broadcast and multicast traffic on network A is no longer prevented from crossing over to network B. You have also lost some security capability.

Keep in mind, this subnet mask setting needs to be applied to each device, not just your PC.

OG