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Old January 13th, 2021, 05:39 PM   #1
graffster
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Message to Different Subnet

Is it possible to message from a CompactLogix on one subnet to a SLC 5/05 on a different subnet routed through a couple of ENBTs in a ControlLogix rack?

I have years of experience setting up messaging to/from CompactLogix ethernet processors through a 1756-ENBT and out a 1756-DHRIO to SLC-5/04s and PLC5s.

I am very familiar with the hardware, software, and networking but have not been able to get it working.
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Old January 13th, 2021, 05:57 PM   #2
Operaghost
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Yes, if the subnet mask for both devices allow it.

Show us an example of the IP addresses and subnet masks for both devices.

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Old Yesterday, 10:27 AM   #3
Nova5
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You can open the range devices can talk to by adjusting your subnet.

The simplest way set the 3rd octet to zero. But this causes a increase in traffic seen by that device.

Say...
Device 1 has a IP of 192.168.1.1
Device 1 has a Subnet of 255.255.255.0

and
Device 2 has a IP of 192.168.2.1
Device 2 has a Subnet of 255.255.255.0


Devices 1 and 2 cannot talk to each other under those conditions unless you set up routing rules in your switch for it.


Now another method.. Adjust Device 1's Subnet.. 255.255.0.0,

Device 1 can now communicate with Device 2. Device 2 however cannot independently talk to device 1. It can respond to Device 1's requests but it cannot initiate its own. to do that you would zero that third octet on device 2.

This however opens the devices to ALL traffic on the second network. You can do some advanced subnetting trickery by using other numbers, its just a bitmask. Don't zero the 2nd Octet on a 192.168.x.x IP, that gets you into public internet routable address space. If you need class A use the 10.X.X.X IP, that entire block is set aside for private networks. 192.168.X.X is mostly intended for small offices, homes, etc. 10.X.X.X for corporations that would easily exceed the capacity if a class C.

Any private network can use any private IP range regardless of what the thought for it was.

https://www.calculator.net/ip-subnet...it=0&x=75&y=21
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Old Yesterday, 05:11 PM   #4
graffster
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First, thanks for the replies. Second, I got it working.

Topolgy: 1769-L27ERM(100.0.0.73/8) --> 1756-ENBT(100.0.0.78/8 Slot 5) --> 1756-A7 --> 1756-ENET(192.168.0.78/16 Slot 0) --> 1747-L551B(192.168.130.50/16)

My problem was getting the path configured correctly; I needed the correct port number to get OUT the second ethernet module in the CLX rack. I knew that port 1 in the path would go toward the backplane but had only tried a 0 to go out the ethernet port when it should have been port 2.

WRONG: 2, 100.0.0.78, 1, 0, 0, 192.168.130.50

RIGHT: 2, 100.0.0.78, 1, 0, 2, 192.168.130.50

-Graffster
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