Help with Corp IT

cncsparky · Jun 9, 2022

IT changed to Cisco switches and we are now getting duplicate IP faults on our PLC's.

1756-EN2T, two MLX1100's, and a panelview.

We are aware of the AB KB article in this thread:

http://www.plctalk.net/qanda/showthread.php?t=103094

They are still asking us to band aid this by disabling the duplicate fault in the PLC. I have not found any way to do this.

Does anyone know of a way to disable the duplicate IP fault in AB plc's?

Thanks!

Nova5 · Jun 9, 2022

disable duplicate IP... ya mean the event that kicks a device off the network? H,,.. no. Tell them to stop mucking up the control system or PEOPLE DIE. They need to take your device IPs OUT of the DHCP range.

cncsparky · Jun 9, 2022

So we have a local IT networking person. But they have to work with a 'Cisco vendor' whatever that means.

My suspicion is that my question is a 'no'. Actually, I'm hoping so. They need to fix their switch configurations ASAP.

dmroeder · Jun 9, 2022

Maybe I'm not following the plot here, but instead if disabling duplicate IP detection, the right answer is stop duplicating IP addresses.

Dropping an office busy body off of the network is fine. Dropping a conveyor of a network that is moving product in an oven can be a problem. As Nova5 pointed out, there are real world consequences for duplicate IP addresses on control networks.

harryting · Jun 9, 2022

Kick IT out. and if you succeed, please tell me how.

ndzied1 · Jun 9, 2022

Agree with the others.

Maybe you could find a way to charge shop downtime to IT. That might catch some eyes....

cncsparky · Jun 9, 2022

I did call AB support and as guessed there isn't a way to disable duplicate IP monitoring.

This is good since it puts all responsibility back to IT land. They constantly point the finger to us(equipment maintenance).

JeremyM · Jun 9, 2022

Duplicate IP detection and response is baked into the EtherNet/IP protocol.

widelto · Jun 9, 2022

Now I'm retired but never, never, let IT people touch or even see your PLCs.
Do not let them enter your control room.
Staying your PLCs way from IT people avoids all kind of problems.
Your PLC network must be independent from intranet.

AlfredoQuintero · Jun 9, 2022

harryting said:
Kick IT out. and if you succeed, please tell me how.

For the sake of curiosity tried to disable the ACD (address conflict detection) instance attribute in CompactLogix and I get "Attribute Not Supported" when sending SetAttributeSingle with value 0x00 to this instance in order to disable it.
It is only possible to disable ACD from remote IOs that may be needed in QuickConnect applications, but the PLC itself does not allow disabling this feature.

As mentioned in an earlier post, the IT person can study the Cisco documentation and learn which IP address ranges to exclude from the DHCP server configurable IP addresses, as to exclude the IP addresses being assigned to the PLCs. This address conflict detection feature is there for a reason.

Nova5 · Jun 9, 2022

cncsparky said:
I did call AB support and as guessed there isn't a way to disable duplicate IP monitoring.

This is good since it puts all responsibility back to IT land. They constantly point the finger to us(equipment maintenance).

There won't be. Its part of the TCPIP stack. Any IT IDIOT that suggests that.. needs to be fired.. They don't have the needed brainpower to avoid catching the berries in their pants zipper

drbitboy · Jun 10, 2022

Nova5 said:
There won't be. Its part of the TCPIP stack. Any IT IDIOT that suggests that.. needs to be fired.. They don't have the needed brainpower to avoid catching the berries in their pants zipper

LOL

and +1
_

robertkjonesjr · Jun 11, 2022

Cisco has an IP device tracking feature that can trigger this. See it all the time. They can disable this feature at the switch port level. A packet capture can prove the fault - look for ARP and the source MAC addresses.

ACD (address conflict detection) is not baked in - there is an RFC for it and many devices don’t do it, or do it right. It is becoming much more common though, but it can be turned off with the right hooks (might need stack level access).

JeremyM · Jun 11, 2022

robertkjonesjr said:
ACD (address conflict detection) is not baked in - there is an RFC for it and many devices don’t do it, or do it right. It is becoming much more common though, but it can be turned off with the right hooks (might need stack level access).

I'm referring to EtherNet/IP (the CIP protocol extension), not the TCP/IP stack. It's a required part of conformance testing.

Saffa · Jun 11, 2022

The Micrologix PLCs at least, do have a tick box in the ethernet channel set up for "disable duplicate IP detection". This just stops the controller from faulting if a duplicate IP is detected. It of course is still very bad if this happens and there's anything talking to the PLC, as communications will be interrupted.

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