Connectivity Issue

Userlevel 2
Badge +7

Good morning Fiixers, I hope everyone is doing well

We are wondering if anyone has ever had issues with adding to many devices to their PLC network. 

Earlier this week, we attempted to add 4 additional devices to our PLC network. We are using an Allen Bradly 1769-L35 PLC to run roughly 32 ethernet connected devices, like Allen Bradley 1734-AENTR remote I/O and PowerFlex VFS’s.

We attempted to add 4 more devices to the network,( All IP’s were pinged before adding the devices ) and the network bricked, it would not allow COMs between the RsLogix 5000 or our Maple HMI Easy Builder software on our computers. Once we remove the devices from ethernet network, and reset the 1769-L35 PLC, ( Dropping out one whole half of the plant ) we were able to establish connectivity again. 

We are operating under the assumption that we exceeded the amount of ethernet devices that are able to run on the Allen Bradly 1769-L35. We do have a call in with support to confirm this assumption, but are wondering it anyone else has experienced these issues. 


Thank you


2 replies

Userlevel 3
Badge +5



It sounds like you are a lot farther ahead of the rest of us.  We are just talking about adding machine metrics to our cleanroom.


Hope you got your devices networked.  Did you get help from FIIX?



I know that this is a bit late to the party, and we aren’t an Allen-Bradly shop, but it sounds like you are dealing with a network traffic issue. With 10/100 networking, you are limited to the number of connections you can have simultaneously and the amount of traffic you can read.

Looking at the guide for the 1769, the max number of ethernet connections is 32 but only if you have the packet interval set for 32 ms or higher. I’ve grabbed this from the manual (Link to PDF)


Connections over an EtherNet/IP Network
You indirectly determine the number of connections the controller uses by configuring the controller to communicate with other devices in the system. Connections are allocations of resources that provide more reliable communication between devices than unconnected messages.

All EtherNet/IP connections are unscheduled. An unscheduled connection is a message transfer between controllers that is triggered by the requested packet interval (RPI) or the program, such as a MSG instruction. Unscheduled messaging lets you send and receive data when needed

The 1769-L32E and 1769-L35E controllers support 100 connections. However, the built-in EtherNet/IP port supports only 32 CIP connections over an EtherNet/IP network. With these controllers, the number of end-node connections they effectively support depends on a connection’s RPI

Requested Packet Interval Max EtherNet/IP Port Communication Connections
2 ms 2

4 ms

8 ms 10
16 ms 18
32 ms+ 25+

You can use all 32 communication connections on the built-in EtherNet/IP port. However, we recommend that you leave some connections available for tasks such as going online and non-I/O purposes.

I’m curious to know what resolved the issue considering this was 7 months ago.



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