You are not registered yet. Please click here to register!

plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
Try our online PLC Simulator- FREE.  Click here now to try it.

New Here? Please read this important info!!!

Go Back - Interactive Q & A > - Interactive Q & A > LIVE PLC Questions And Answers

Thread Tools Display Modes
Old January 13th, 2021, 05:39 PM   #1
United States

graffster is offline
Join Date: Mar 2011
Location: IL
Posts: 2
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.
  Reply With Quote
Old January 13th, 2021, 05:57 PM   #2
United States

Operaghost is offline
Operaghost's Avatar
Join Date: Apr 2002
Location: Dallas, TX USA
Posts: 2,992
Yes, if the subnet mask for both devices allow it.

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

I despise when people take random quotes and ascribe them to me - Julius Caesar
  Reply With Quote
Old Yesterday, 10:27 AM   #3
United States

Nova5 is offline
Join Date: May 2013
Location: Panhandle TX
Posts: 221
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.

Device 1 has a IP of
Device 1 has a Subnet of

Device 2 has a IP of
Device 2 has a Subnet of

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..,

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.
  Reply With Quote
Old Yesterday, 05:11 PM   #4
United States

graffster is offline
Join Date: Mar 2011
Location: IL
Posts: 2
First, thanks for the replies. Second, I got it working.

Topolgy: 1769-L27ERM( --> 1756-ENBT( Slot 5) --> 1756-A7 --> 1756-ENET( Slot 0) --> 1747-L551B(

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,, 1, 0, 0,

RIGHT: 2,, 1, 0, 2,

  Reply With Quote
Jump to Live PLC Question and Answer Forum


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Im totally new! Please help! Tool changer PLC mike^3 LIVE PLC Questions And Answers 34 November 3rd, 2015 04:28 PM
Limit RSLinx to a single IP address on a network adapter EuanK LIVE PLC Questions And Answers 6 January 22nd, 2010 09:22 AM
Control logix to slc 505 message instruction failure kentuckytech LIVE PLC Questions And Answers 5 December 1st, 2008 07:08 AM
transmitting a message on a cp340 with 3964r anotherone LIVE PLC Questions And Answers 0 November 25th, 2006 08:07 AM
Locale message display problem RSView Studio mulderm LIVE PLC Questions And Answers 16 November 13th, 2006 07:47 AM

All times are GMT -5. The time now is 07:27 PM.