Article: KB-10828
Resolve Duplicate IP Detection Faults on ControlLogix and CompactLogix PLC interfaces caused by network switch replacement.  Known equipment affected: 1756-ENBT, 1756-EN2T, 1769-L32E, 1769-L35E.  Other Allen Bradley processors and/or Ethernet interfaces may be affected.
Skill required to complete this article: Administrator and level is Expert.

Multiple Intelligrated customer sites have reported significant downtime following replacement of network switches (specifically Cisco, but others may employ similar technology), when most or all Logix5000-based PLCs experience communication shutdowns due to 'Duplicate IP Faults'. 
Symptoms vary between ControlLogix and CompactLogix PLCs in that their Ethernet Interfaces are different.  The issue is believed to be related to IP Device Tracking functionality employed by default on many newer Cisco network switches.  The symptoms below have been known to subside for up to 30 minutes following restarts of the PLCs in question, only to return repeatedly until a solution is implemented on the network switch.

Symptom details:
ControlLogix 1756-ENBT, 1756-EN2T and other adapters include an LED ‘screen’ where they typically scroll their IP address and any other status information.  When experiencing the problem scenario, they will display ‘Duplicate IP Detected' as part of the scrolling error message.

CompactLogix 1769-L32E and –L35E Processors include the Ethernet interface on the processor, and do not scroll any information, but display a SOLID RED NS (Network Status) and FLASHING RED MS (Module Status) indicator LEDs.  When in the faulted state, both of these interfaces shut down and do NOT respond to PING or any other Ethernet traffic.

Cisco has released 2 documents through their Technical Assistance Center (TAC): 118630 includes information on IP Device Tracking (IPDT), which is believed to be the primary culprit of these problems.  116529 is a Troubleshooting page including steps to resolve the issue.

Rockwell Automation has also released knowledgebase article 568750 (login required).  The text of this article may be found here (effective 4/26/2015): 568750 2015 0426.

For Intelligrated Technical Support: TS-00267749 is a master incident related to this issue and contains links to multiple related incidents at customer sites.


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Published on 5/4/2015.
Last Modified on 5/4/2015.
Last Modified by Kurt Kimnach.
Article has been viewed 10091 times.
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