PLC network question

Please see attached drawing, there are 3 switches, 2 IP for each switch, and there are 4 PLCs(Contrologix) connected with switches. we need send data back to 10.1.1.40 PLC from others. we could setup a trunk between switches so 10.1.1.40 could get message from 10.1.1.50. my question is how to setup the communication in order to get data from 10.0.3.30 and 3.0.1.78? do we need 2 ether net module in 10.1.1.40 rack?
thanks

ControlLogix CPUs do not have an Ethernet port(hence there is no IP Address attached to any CLX CPU!); they are using Local Chassis installed 1756 bridges in order to communicate over Ethernet.
In order to establish communications between the four controllers, each CLX Local Chassis will need an installed 1756 bridge and the four dedicated bridges will have to reside within the same logic subnet (the IP Addresses of the inter-CLX communications bridges will have to carry addresses containing identical first three octets (10.1.1.xyz, 10.0.3.xyz, etc.).
Once there, there is a matter of patching all four bridges together; unmanaged switching will suffice.

sorry for the confusion, there is a ethernet module in each PLC rack. i mean do i need to add another 2 ethernet module in 10.1.1.40? one for 10.0.3.30, one for 3.0.1.78.

thanks

...but the four "chosen" 1756 bridges do not have compatible IP Addresses (except for 10.1.1.40 and 10.1.1.50).
In order to be able to communicate in between, the four 1756 modules intended to be used for CLX-to-CLX communications will have to have identical first three octets (sets of numbers between the "points")within their IP addresses.
Since two of the installed ones already have "non-compatible" addresses with the 10.1.1.40 and 10.1.1.50 bridges and since they are probably already used for other purposes, you will have to add two other bridges (within the Local Racks of the other two CLXs) and set them up as 10.1.1.111 and 10.1.1.222 for example.
When all four bridges will have IP addresses such as 10.1.1.40, 10.1.1.50, 10.1.1.111 and 10.1.1.222 for example, you are ready to communicate.

are we talking about the same thing in different way? im thinking about add 2 bridges in 10.1.1.40 rack, with IP assdess 10.0.3.31, and 3.0.1.79 for example.

thanks

Please take this in a constructive and positive sense. I'm sure you are an expert in other matters.

But the questions you are posting indicate that you are in over your head with IP network communications. The questions you are asking are far more fundamental than "help me configure a MSG instruction".

You need to bring in somebody who understands basic Ethernet and IP architecture and have them help you build this system. Your company probably has an "IT guy" or "Network guy". In my city, you can't buy a cup of coffee without encountering a freelance IT consultant.

The tipping point for my advice is that one of your IP addresses, 3.0.1.78, is actually a public Internet address belonging to General Electric. Using a public address in a private network is a fundamental error.

hi Ken

I just know it not a PLC (3.0.1.78), actually it is a HMI and the IP will be 3.0.1.67, I understand what you are talking about private and public network. please just look the case as an example, in order to message between 3 different networks, is the method we mentioned before correct?

thanks

angi said:

just look the case as an example, in order to message between 3 different networks, is the method we mentioned before correct?

Click to expand...

Define 'correct'? Is it correct in that it will work? Yes. Using additional bridges will get you there.

Is it correct in the sense of being the 'right' or 'best' method? I'd say no. Of course that is just the opinion of some random dude on the internet.

Take the example of a home network. You want to be able to communicate with a printer, another computer and the internet (all on differing subnets). You would not keep on adding NICs for each subnet, would you?

I'd argue your 'correct' solution is a layer three switch. Properly configured, it will allow traffic to pass from one subnet to another.

In the future someone wants to add another PLC, using bridges means you need another bridge. Using a switch wouldn't require anything more than configuring an unused port.

I wholeheartedly agree with Ken. Find yourself someone who does this for a living. You don't let the civil engineer design your control system, don't be afraid to let an IT guy design your network.

Thanks Tim, Dmarg and Ken!

Timbert said:

Define 'correct'? Is it correct in that it will work? Yes. Using additional bridges will get you there.

Click to expand...

Tim,
Not to hijack this thread, but I need to confirm what a "Bridge" is.
Is this an ENET or ENBT module in this case ?

passwordg said:

Tim,
Not to hijack this thread, but I need to confirm what a "Bridge" is.
Is this an ENET or ENBT module in this case ?

Click to expand...

The ENET is not a bridge.

If we look at the original post (and I understand it correctly) the user wants PLC 10.1.1.40 to talk to the other PLCs (10.0.3.30 and 10.1.1.50) and HMI (3.0.1.78).

I believe this could be done with ENET as there is no requirement that a PLC be able to talk with I/O on another subnet or anything other than 10.1.1.40. In other words, no bridging takes place. But if PLC 10.1.1.50 needs to talk with the HMI 3.0.1.78 then a bridge is needed to make this happen it will require ENBT modules.

I'll be honest I've never worked with the old ENET or tried to configure bridging networks. I've used switches and routers.

This is what Rockwell has to say:

Routed connections on a convoluted network such as multi-hopping 1756 chassis may not be stable, because the 1756-ENBT/Ethernet modules are not designed as routers. Good network design practice should keep network hops to a minimum and use true routers to partition networks. (KB 26787)

Click to expand...

1756-ENBT, 1756-EN2T, 1756-EN2TXT, 1756-EN2TR, 1756-EN3TR are all commonly refered to as bridges since they are used to "bridge communications between the CPU and the subnet patched within"

To add my $.02 - Ken and Timbert are correct. To be blunt, based on what you've shown, your IP addressing scheme appears to be nonexistent (all jacked up). Your best bet is to go to your IP department for help and come up with a useful scheme.

FYI, a router or layer 3 switch (both provide the same functionality for this example) can pass traffic between different logical networks, such as the ones you have. In this case you would still probably need to edit the IP settings on your devices to enter their respective "default gateways". As long as you're doing that - you might as well correct the addresses.

Out of curiosity, what subnet masks are you using?

Whenever I have encountered 3.xxx.xxx.xxx IP addresses employed in a control system network, it tends to trace back to a programmer inexperienced with Ethernet setting up Ethernet communications with a GE Fanuc PLC according to examples given in the GE user manuals.

Why don't you simply reassign all of your IP addresses within the range of 10.0.0.1 through 10.0.0.254? you are making this much more complicated than it needs to be.