Allen Bradley Ethernet/IP quickie


Thread Starter



I'm having difficulty with my first Ethernet/IP application. I've a ControlLogix 5561 controller with an IP card communicating with 2 external I/Os. It also communicates with a PanelView700 HMI.

The PanelView is retaining its designated IP settings after boot or reset.

The other 3 devices (PLC and 2 I/Os) require IP settings to be set from a laptop using BOOTP software.

All the devices are configured correctly and communication is unfaulted once set up from BOOTP.

The hardware config within the RSlogix program is correct also and details each device's IP address.

My question is basic, why is the PLC not reading its own IP settings from the installed program and should it not write this data to the I/Os also at power up instead of going into BOOTP mode?

James Ingraham

1) Use the bootp server software provided by Rockwell.

2) After assigning an IP address, right click on the device.

3) You'll get an option to turn off bootp

That should do it.

-James Ingraham
Sage Automation, Inc.

curt wuollet


How would it know what addresses to write to if the other have their address set by bootp? You almost have to run all dynamic addresses with DHCP or BOOTP. You can configure the RA server to assign "static" addresses by MAC number. But, yes, this can be a PITA. I think the idea is to run the RA server for your automation network.


David Ferguson

More information is needed, which PLC is losing it's IP (Brand), if another AB processor, there is a place to "hard code" the address.

I guess I am a little confused as to what is losing its IP. I assume it is the other PLC and not the controllogix card (which is settable to be hard coded).

Dave Ferguson
In Allen-Bradley ENBT modules, not only must you set an IP, you must TURN OFF BootP. This can be done through the BootP utility or through RSLinx.

You also asked about the IP address configured in the PLC program. When the ENBT module is listed in the program's I/O tree, the IP address listed in that module's properties ultimately has nothing to do with the actual IP address configured in and used by the module. Meaning, if you change the IP address in the properties of an Ethernet module in the PLC program, then download the PLC program into the PLC processor, that will NOT set the IP address of the Ethernet modules.