Is this an error message? A notice?? What does it mean?

Question

Every day for the last two weeks or so I've been having the same thing happen. When I leave my computer on but unattended for several hours (maybe 6+, like while I'm at work or sleeping), when I come back to the computer, there's a message on my desktop that says: "192.168.1.100 in use by 00:21:5c:0b:f8:a7, DHCP Server 192.168.1.1" And there's an exclamation point in a red box to the left of it.
What the heck does that mean?? And do I need to do anything about? I wonder why such cryptic messages are even made!
Thanks!
P.S. Yes, I've rebooted, and no that hasn't changed anything.

Answer 1

Hi,
Yes, use of the term "machine" is meant to explicitly avoid implicating only computers! If your printer is networked, then it has an IP and must be considered a suspect. That is to say that if it connects to your home Internet router/hub via an Ethernet cable or WiFi, it has an IP; if it connects directly to a computer via USB it almost certainly does not.
Since the offending device was manufactured by Intel, and since Intel makes both wired and wireless NICs, I would start with your husbands computer. Do you know how to display IP addresses on both computers? It varies by operating system but it can be done fairly simply regardless. In Windows, I just launch a "Command Prompt" (under Accessories or Run>cmd) or and issue 'ipconfig' and then just look for that duplicate IP address. In OS X, you need a terminal shell and issue 'ifconfig' and repeat the same process (depending on the number of NICs installed, you may have to wade through a bunch of nonsense but your main goal is just to ensure you don't see that common IP showing up twice). Of course there are more graphical ways to do both but that'll take a fair bit of explanation, so try to go with this path of least resistance.
If you do in fact find a duplicate, you'll have to decide how to fix it. Hard-coding one machine for a similar but not exactly identical address would be one choice. Implementing DHCP would be a much better choice but you'd need to ensure something in your network will act as a DHCP server. Most everything sold in the past decade will.
And I should say again that your specific network environment may lead to a different conclusion about what exactly is going on. I gave you my best guess based upon the information available. As a general disclaimer: I'm a network engineer by trade but I'm by no means an OS X expert, so that error message might somehow be misleading me. I doubt it highly, but can't rule out entirely that it might be...
Regards,
Scott