Cisco C2960X - clients getting DHCP errors

[it inx]

Hello, i am having issues with connections on our 4 stack switches C2960X, Windows clients getting errors on startup or on reconnecting to the network and are not receiving a DHCP address of our Windows DHCP server. They are getting an automatic ipaddress 169.x.x.x, when doing ipconfig /release and renew, then they get an ipaddress of the DHCP server.

The error in the clients System - Eventlog is id:4199. It says that there is an ipaddress conflict with an other device, and the macaddress of that "other device" is in fact the lan-interface of the switch where the computer is connected. 

The system has detected an address conflict for the IP address 10.0.13.2, where the system has the network hardware address 00-41-D2-DA-54-11. This may disrupt the operation of the network on this system.

So why is the lan-interface of the switch holding the ipaddress?

When testing on a different VLAN and with another DHCP we are getting the same errors, so i don't think the problem is the DHCP server.

We have many more other Cisco C2960X switches, clients on those switches are getting without any problem DHCP addresses from the same DHCP-server.

Anybody know what the issue could be?

Kind regards

[Mark Elsen]

 - @it inx  Could you show the running  configuration of that particular lan interface

 M.

[it inx]

Hi Mark, in attachment printscreens of that partical Lan interface.

[Mark Elsen]

  - @it inx     Is there perhaps a conflict in address ranges used for switches and interface 
                               and address ranges used on your DHCP server for PC's ?

  M.

[it inx]

Hi @Mark Elsen , i don't think it is an ipaddress conflict in ranges. Other clients on other switches have no problem.

[Mark Elsen]

  - @it inx                 >... i don't think it is an ipaddress conflict in ranges.....
                    Well as a network administrator you need to know which network ranges are used for switches 
                    and what ranges are used for PC's on the DHCP server , then you must make sure that there 
                    are no conflicts,

   M.

[it inx]

Hi Mark, i am sure that there are no DHCP conflicts. Our switches have fixed ipadresses and do not use DHCP addresses. The macaddress that is holding the ipaddress (when my client is not receiving the ipaddress) is the macaddress of the lan interface from the switch. Each lan port on the cisco has a macaddress, you can see that in printscreen. The port Gi2/0/17 is the lan port for my device. In the eventviewer of windows 11 you see that same macaddress is causing the issue.

[Mark Elsen]

  - @it inx   Can you confirm , that when using ipconfig /release and renew, then they get an ipaddress of your
                  intended  Windows  DHCP server  (by checking the DHCP allocation logs on it)?
                  Well even if that would be the case , it's still possible that initially you would have a rogue DHCP
                  server on the network handing out wrong addresses. In that case you would need to 
                                         configure DHCP snooping on the switches.

  M.

[it inx]

@Mark Elsen , yes we are sure that when doing an ipconfig /release and renew, we get an ipaddress of our intended Windows server. If there is a rogue DHCP in our network, we would also have this problem when we are connected to other switches and that is not so. When putting a simple switch in between it also works fine, a rogue DHCP server would also interfer in that case.

[Mark Elsen]

  - @it inx   In the case of ipconfig /release & renew :  what IP address is the windows DHCP server allocating for the PC ?
                             You can check that by examining the DHCP logs on the windows server

  M.

[it inx]

@Mark Elsen when disabling my LAN adapter in Windows and enabling it again, i have the issue. Ipconfig shows APIPA address (printscreen 2025-10-24 09_10_48 )Log in DHCP server: 2025-10-24 09_12_41.png . When again disabling and enabling i get my ipaddress (2025-10-24 09_15_06.png) and in log DHCP see printscreen 2025-10-24 09_17_25.png.

[Mark Elsen]

    @it inx                                >.....see printscreen 2025-10-24 09_17_25.png.
                        There you see that the  IP address allocated for the  PC by the  DHCP server is the same
                        as the switch interface address!!   So must use another subnet for the PC's (another address range)

   M.

[it inx]

hi @Mark Elsen , you are wrong about the switch interface address. Each lan interface (on our switch 48 ports) have their own macaddress (see printscreen), and it is that macadress that is holding my ipaddress that is assigned to my laptop. Our managment interface of the switch is 10.0.8.220. The managment interface has nothing to do with this. So the question is, why is the lan interface (port Gi2/0/17) holding my ipaddress ?

[Mark Elsen]

  - @it inx                                          I am not yet completely convinced; originally  you wrote :
                     >...The system has detected an address conflict for the IP address 10.0.13.2, where the system has the network hardware address 00-41-D2-DA-54-11. This may disrupt the operation of the network on this system.

                        00-41-D2-DA-54-11 belongs indeed to a Cisco device (checked with https://macvendors.com/ )

                        As a test ; on the DHCP configure a complete other mac address for the PC
                        such as 2.17.198.195  , that's a public address but that doesn't matter for the moment
                                                 (I want to exclude confusing APIPA messages).

                        The PC won't be able to do anything with that address on your network obviously.
                        The idea is to check whether the PC will still report the same errors when this is done, or not

  M.

[it inx]

@Mark Elsen , i assume you suggest to assign a complete other ipaddress for the pc and not a complete other mac address. But on our Windows DHCP server it is not possible to make an ip reservation (based on the macaddress of my pc) in a complete other subnet. What i did test was to assign my lan port 2/0/17 to another VLAN (vlan192), and on that VLAN192 there is an other DHCP server active (our firewall's dhcp server), it gives me the same issue.  00-41-D2-DA-54-11 is then also taking the ipaddress 192.168.3.x that was assigned to my pc. So the issue is also not the DHCP server.