Another duplicate IP address issue on an AB network

Kip Williams · Sep 16, 2022

I have a process network connected together with N-Tron unmanaged switches consisting of two CompactLogix PLCs, a 1794-AENT remote IO rack, two red Lion HMIs, and a gateway rack (ENBT&DHRIO) that’s talking to 4 SLC 5/04s over DH+. The network is then connected back through a Cisco Catalyst 2960 switch over VPN to a SCADA system running on a server 300 miles away. This system has been running flawlessly for about 5 years, and then about a month ago we started receiving duplicate IP errors on both the gateway rack AND the remote IO rack (there are no duplicate IPs). The system runs fine if we disconnect it from the Cisco switch and the SCADA but if we connect either the gateway rack OR the remote IO rack back to the switch then we get a dup error on the connected device.

I am completely aware of the service bulletin regarding Cisco or Stratix switches with IP device tracking.. however there have been no recent changes made to the network or updates to the switch (the last power cycle was over 6 months ago). Additionally, we have checked switch settings and confirmed that this isn’t the issue…

However, I’m now wondering if it's possible for a switch or router on the ISPs network to be causing this issue. AB tech support says no, but I’m at a complete loss about what else it could be. And if this something caused by something outside of my control, what's the solution... other than 300 miles of cable or moving the server to the remote facility.

dmroeder · Sep 16, 2022

What IP address range are you working with? I've seen a number of people using public IP addresses on their private network. Without thinking too deeply about this, that seems like a potential for problems.

Kip Williams · Sep 16, 2022

IP addresses are non-public (10.99.26.xx), and we have also verified that there are no DHCP servers active on the network.

James Mcquade · Sep 16, 2022

try this,

locate the device on your system with the ip address that had a duplicate.
disconnect it for 30 seconds.
reconnect it, it should work for about 5 minutes, then fail.
if you do this more than 2 times, there is a duplicate ip address on the network somewhere.
i ran into this 4 years ago, someone broke a display banner and grabbed one out of the scrap pile that still worked. it was a duplicate ip address of one of our barcode scanners. i had to create an entirely new range for our scanners to avoid conflicts.
james

tom_stalcup · Sep 16, 2022

Kip Williams said:
I have a process network connected together with N-Tron unmanaged switches consisting of two CompactLogix PLCs, a 1794-AENT remote IO rack, two red Lion HMIs, and a gateway rack (ENBT&DHRIO) that’s talking to 4 SLC 5/04s over DH+. The network is then connected back through a Cisco Catalyst 2960 switch over VPN to a SCADA system running on a server 300 miles away. This system has been running flawlessly for about 5 years, and then about a month ago we started receiving duplicate IP errors on both the gateway rack AND the remote IO rack (there are no duplicate IPs). The system runs fine if we disconnect it from the Cisco switch and the SCADA but if we connect either the gateway rack OR the remote IO rack back to the switch then we get a dup error on the connected device.

I am completely aware of the service bulletin regarding Cisco or Stratix switches with IP device tracking.. however there have been no recent changes made to the network or updates to the switch (the last power cycle was over 6 months ago). Additionally, we have checked switch settings and confirmed that this isn’t the issue…

However, I’m now wondering if it's possible for a switch or router on the ISPs network to be causing this issue. AB tech support says no, but I’m at a complete loss about what else it could be. And if this something caused by something outside of my control, what's the solution... other than 300 miles of cable or moving the server to the remote facility.

I managed to trigger the issue on our network with the IP device tracking a few years back....

I'd connected a laptop to the network (ethernet) that had a network bridge setup between the ethernet and the wifi. As soon as I plugged it back into the ethernet cable, it triggered the (false) duplicate IP address failures on 3 unrelated stratix switches on our network.

Kip Williams · Sep 16, 2022

Tom, with two different devices faulting at exactly the same time, I do feel like its related to device tracking; but I didn't consider a bridge as being a possible cause. I will have the team investigate that possibility on Monday. Thanks for the input!

ASF · Sep 18, 2022

Last year I had a strange issue that presented as duplicate IP addresses being detected on a network where there were none. I can't say for sure that the same thing is happening to you, but given that you have similar symptoms and no obvious answer, it's worth at least considering. Post here

Jmeadows7676 · Sep 19, 2022

I would say that the ENBT cards are below version 6.006. This happened to me last year and I fixed it by upgrading the Firmware to the latest. The Newer Cisco switch is putting out some protocol that the ENBT doesn't understand. Did someone upgrade the Firmware on the Cisco Switches?? That is what started this problem with me.

Contr_Conn · Sep 19, 2022

Update to 6.006 should resolve this.

Also see Rockwell Technote BF 2882 - Access Everyone
False Duplicate IP Detection on Ethernet Modules with IP Device Tracking Enabled:
https://rockwellautomation.custhelp.com/app/answers/answer_view/a_id/568750

Kip Williams · Sep 29, 2022

Thank you everyone for your suggestions!! The update to 6.006 did in fact resolve the problem. Thanks!!!!

Another duplicate IP address issue on an AB network

Kip Williams

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dmroeder

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Kip Williams

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James Mcquade

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