If you see mysterious IPs on the network – and they don’t seem to be actually be doing anything like SMTP or DNS or SSH, there’s an angle you may not have considered.
Do a Google search for the address and the word “default” and see if anything is using the IP address for a default setting. Many routers or other devices come with a default setting and you may have one or more of these on your network which has not yet been configured.
In my case, the culprit was the IP 192.168.0.120 – which turned out to be a Dell iDRAC which was not yet configured.
UNIX Administratosphere 