One mac address is seen on two differnet ports

[Pune-Netops]

The system was getting APIPA ip add. After logging in to the switch we fonud the following output : -
Vlan Mac Address Type Ports
---- ----------- -------- -----
20 7085.c281.66bd DYNAMIC Gi1/0/34
30 bd7085.c281.66 DYNAMIC Te1/1/1

We checked the dhcp logs for deep scanning . Below is the output :-
Oct 8 16:00:06 dhcp dhcpd[2829535]: DHCPACK on 192.168.20.23 to bd7085.c281.66 (DESKTOP-4CBV21L) via 192.168.20.1

Oct 8 16:00:06 dhcp dhcpd[2829535]: DHCPREQUEST for 192.168.20.23 (192.168.40.254) from bd7085.c281.66 (DESKTOP-4CBV21L) via 192.168.30.1: wrong network.

Oct 8 16:00:06 dhcp dhcpd[2829535]: DHCPNAK on 192.168.20.23 to bd7085.c281.66 (DESKTOP-4CBV21L) via 192.168.30.1

Oct 8 18:02:33 dhcp dhcpd[2829535]: DHCPACK on 192.168.20.23 to bd7085.c281.66 (DESKTOP-4CBV21L) via 192.168.20.1

Oct 8 18:02:33 dhcp dhcpd[2829535]: DHCPREQUEST for 192.168.20.23 (192.168.40.254) from bd7085.c281.66 (DESKTOP-4CBV21L) via 192.168.30.1: wrong network.

Oct 8 18:02:33 dhcp dhcpd[2829535]:DHCPNAK on 192.168.20.23 to bd7085.c281.66 (DESKTOP-4CBV21L) via 192.168.30.1

Please help us in troubleshootinh the issue .

@M02@rt37

@community centre

[David Ruess]

Hello,

It looks like one of your devices is trying to use an IP address that's not in its proper subnet. You can see there is a Negative ACK (NAK) saying you can't use that IP.

Make sure the device isn't holding on to an old IP or that its manually configured (shouldn't be since its sending DHCP messages).

Clear the IP on the device and reboot it and see if that fixes the issue. Also clear the ARP cache on the network device.

-David

[Pune-Netops]

As checked there is no static ip add configured on the device .

We have clear the ARP cache on the network device .

[MHM Cisco World]

This PC of ipphone ? And these vlan20/30 is voice/data vlan?

If Yes then it SW bug.

MHM

[Pune-Netops]

The device is a windows system .

And these vlan20/30 is voice/data vlan?  only data vlan

20 7085.c281.66bd DYNAMIC Gi1/0/34 ( access port )
30 bd7085.c281.66 DYNAMIC Te1/1/1   ( Trunk port )

[MHM Cisco World · Accepted solution]

Most likely it issue of native vlan mismatch in trunk between SW 

MHM

[Pune-Netops]

Thank you for  the reply we will troubleshoot and will update for the  same .