We have a network with a bunch of 3560 switches setup and desktops/laptops and some Rockwell Automation equipment connected to them. We had to add a new switch, a 3560X to the network recently to add capacity. After adding this switch, a bunch of the Rockwell Automation devices detect duplicate IPs from the MAC of the new switch. This does not occur with any desktops/laptops/printers/etc. The issue happens to Rockwell equipment plugged into 3 different switches.

All wired ports use vlan 101. It is on subnet:

All network devices are on vlan 2 for management. Subnet:

The new switch did have an interface on vlan 101 without an IP assigned (mistake) which I removed recently but the issue persisted. I am rebooting the switch now as at least on the routers, the interface persists in a deleted state until a reboot.

I am going to be setting up an RSPAN for the ports with equipment having the issue next if this persists after the reboot.

What would cause end user devices to think a switch has the same IP as them? We have not had this issue at any other site with the same setup.

Switch layout:

switch-stack1 -G1/0/10----G0/1-> switch2 -G0/2----G0/1 -> switch3
                                 switch2 -G0/3----G0/1 -> switch4

switch-stack1 -Gi1/0/6----G0/1-> switch5

switch-stack1 -Gi1/0/5----G0/1-> switch6 -G0/3--G1/0/1 -> switch7

switch-stack1 -Gi1/0/4--G1/0/1-> New switch causing problem

switch-stack1 -Gi1/0/1----G0/1-> switch8
  • We may need to see the config of the switch. But a shot in the dark, is proxy-ARP enabled on the 3560X?
    – YLearn
    Mar 4, 2014 at 0:00
  • Hi, it's kindof hard to understand the relationship of subnets to topology from your ascii diagram. Would it be possible to either overlay the subnets on there, or (better) give us information about how each switch is configured? This is going to be a complicated problem to untangle without more specifics about each switch. Also see the NE question checklist Mar 4, 2014 at 10:10
  • We met the same issue with Rockwell Ethernet module 1756-ENBT series A (firmware v 4.002) , we resolved the problem by updating the firmware to v.6.005.
    – user28366
    Aug 3, 2016 at 14:03

2 Answers 2


Hope this helps as I had the same issue and this corrected the problem.

568750 - False Duplicate IP detection on Logix Ethernet modules when used with Cisco switches Access Level: Everyone Date Created: 10/22/2013 10:54 AM Last Updated: 08/27/2014 10:33 AM

Problem When Logix Ethernet modules are connected to a subnet containing Cisco switches with "ip device tracking" (IPDT) enabled, the modules may go into a duplicate IP address state after a restart/reset.

Environment Any layer two networks that contain both Logix Ethernet modules and Cisco switches running IPDT. IPDT is much more likely to be implemented on Cisco switches as of August, 2013 because of a behavior change which enables this command if any feature which requires it is enabled. This behavior change also removes the ability to turn off IPDT without first turning off any features which require IPDT.

The Stratix line of switches will not have “ip device tracking” enabled by default until a permanent solution is in place.

Cause The IPDT feature sends probe ARP packets with a source IP address of, the source MAC ID of the switch, and the target IP and MAC ID for the device being probed to check that it is still connected and responsive.

When a device becomes disconnected, and then is reconnected within the configurable IPDT timeout period, probe ARP packets may be received by a Logix Ethernet module at the same time as it is in its Address Conflict Detection mechanism. If this happens, the Logix Ethernet module will immediately go into a duplicate IP state, and stop communicating.

IPDT when activated on a Cisco switch will try to probe for every ip connected on the subnet, regardless of whether it is connected to that switch or not. Testing has shown that this affects the majority of Ethernet modules sold by Rockwell Automation.

Workaround Several workarounds to this issue exist. They all make suggestions using Cisco IOS command-line interface commands.

Workaround 1 Architect manufacturing zone subnets such that: 1. IPDT is explicitly disabled on every trunk port with the following command:

Hostname (config-if)# ip device tracking maximum 0 2. IPDT probe delay is manually configured on any access port connected to a Rockwell Automation Ethernet module with the following command:

Hostname (config)# ip device tracking probe delay 10 Workaround 2 If the switch in question has an administration IP (SVI) configured on the subnet/VLAN in question the Cisco CLI command:

Hostname (config)# ip device tracking probe use-svi will insert the administration IP into the source IP in the IPDT packet. This packet will not impact Address Conflict Detection operation.

Workaround 3 Disable IPDT on any Cisco switch ports with IPDT enabled that subsequently connect to a Rockwell Automation Ethernet module with the following command:

Hostname (config-if)# ip device tracking maximum 0 Solution The permanent solution is under consideration.

Comments (1)

jbrodsky 06/04/2014 08:13 AM This command does not work in all Cisco switch firmwares.

The command that worked for me was

Hostname (config-if) # nmsp attach suppress

and I later confirmed that it worked by issuing the following command

Hostname # show ip device tracking all

and the device should NOT show up in the list of enabled devices.

The alternative command that others have used to disable IP device tracking is Hostname (config-if) # no ip device tracking max

But that had no effect for me using a 3850 stack with version 3.02.03.SE The command was accepted but did not disable anything when I checked with showing device tracking.

Be forewarned that Cisco is having complaints about this issue and they are probably going to change the firmware yet again... Reply | Flag as Inappropriate | Post a Comment Product Tree for This Answer (expand/collapse)Expand Product Tree for This Answer ID Answers others found helpful

35072 - EtherNet/IP Duplicate Address Detection 118216 - Logix modules Duplicate IP address detection enhancement 51541 - 1756-ENBT display Duplicate IP scrolling over display 573991 - Unknown multicast traffic flooding network with 1783-ETAP with IGMP 42616 - IP addresses of Ethernet modules in a Redun

  • IP Device Tracking/NMSP affect PLCs in automated production network. As jbrodsky mentioned, Cisco 3850 uses IOS-XE which has a somewhat different command set for some commands. Sep 16, 2014 at 14:28

[Sorry, worke intruded]

IP Device Tracking/NMSP affect PLCs in automated production network. We had an issue too when adding a new 3850 to a network and the PLCs started reporting Duplicate IPs with the 3850 MAC, when that switch didn't even have an IP on that subnet.

Add to this that the Dupes weren't reported immediately, but had a 5-35 minutes delay after booting.

I lost two days troubleshooting this, after opening a TAC, the Cisco engineer found the problem in less than 15 minutes.

New Feature... new Active by Default Feature... which isn't easily linked to the symptoms when you first encounter it


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