why does my iMac has two IP addresses registered?

Solution 1:

I have 4 IP addresses on some of my Mac's network interfaces since I set them up in network preferences control panel.

You could go there and delete all un-needed IP addresses or at least know it's not something that was intended.

Solution 2:

Depending on you LAN setup, this can happen if the computer has ethernet and wifi both turned on.

You can verify from the Mac in System Preferences->Network: if both Ethernet and Wifi are green that's it.

In this case the Mac will use the first one listed--- either make sure the faster connection is first or turn off the slower.