flapping between port

[GM01972]

Cisco C1000-48P-4G-L
Hi I just unpacked this switch and am getting a lot of these error messages.
Host 0026.xxxx.93a4 in vlan 1 is flapping between port Gi1/0/2 and port Gi1/0/1

Gi1/0/1 is PC
Gi1/0/2 is connected to an unmanaged switch which at this point is kind of the nucleus of our small network.  Router and Windows AD/DC are plugged into the unmanaged Netgear switch.

I do not want to setup any VLANs or anything fancy at this time. Why am I getting error in the log like the one above? This happens for multiple devices plugged into the new Cisco switch. The MAC address in the error  is the MAC of the PC connected to the new switch.

[julian.bendix]

Hi!

Well the Log appears because it seems that the Switch is also receiving frames with the MAC address of the PC as source on the port where the unmanaged switch is connected on.

Very fast guess: Could something loop packets on the unmanaged switch?
It could be that there is a network loop on the unmanaged switch and therefore packets coming from the Cisco Switch are looped back.

Best regards
Julian

[GM01972 · Accepted solution]

Yes, I understand that flapping has something to do with looping packets. I have not found a way to resolve this. We moved into our production setup where the Cisco C1000 is our primary switch with the router and AD/DC plugged right into it and then a couple other unmanaged switches linking back to the C1000. This works and we are not getting any errors.