some devices have a "shared management network port" that is : one physical port with two network controllers attached internally.
- one for data
- one for management (frequently web based managment).
Look if your dhcp-server shows a lease for this Mac address.
and open
http://<IP-ADRESS> to verify if this is a management interface.
Many servers offer such a shared port.
some of your options are:
- disable the management interface
- configure the management interface to use vlan-tags
- configure the device to use two different physical connections (if present).</IP-ADRESS>