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Q: I was recently a guest at a hotel that had internet provided in each room. I had my laptop computer connected to the internet and for 2 days had no problem. On the 3rd day every time I tried to access the internet, I got a message that said some computer on the network had the same IP address as mine, and I could not access the internet. How can this be?

– Jan E.
Crestview, Florida

A: Quite easily, Jan. Before I answer, let me give my usual background information for the jargon-challenged among my readers. An IP address, or Internet Protocol address is a numeric label assigned to any device that uses the Internet Protocol language to participate in a network. Without delving into how IP addresses work, let’s just say they are to your computer what the numbers on the front of your home are to your house. They tell everyone where that device is, and uniquely identify it among all the other devices on the network. Now, IP addresses come in 2 types: “static” addresses that don’t change (which are usually used only in corporate networks) and “dynamic” addresses, that are automatically assigned by something called a Dynamic Host Configuration Protocol (DHCP) service. Using DHCP, your computer basically announces to the network that it is there, and needs an address. The DHCP service assigns the next unused address in its list of addresses. Depending on how the DHCP server is configured, these IP addresses periodically expire, and are returned to the pool of available addresses, to be assigned to another machine.

So, what I think probably happened is that you got online at the hotel, and your machine was assigned an IP address. Then, at some point when your computer was idle, the address expired on the DHCP server. Your computer may have been in sleep or hibernate mode, and would not have been notified that its IP address needed to be renewed. Meanwhile, someone else’s computer, was assigned the IP Address that was freed from your computer. When your computer came back up, it attempted to use the formerly assigned address, only to find that another system on the network now owned it. If it’s any consolation, the owner of that computer likely received a similar message to what you got. The solution to the problem is to simply renew the IP address. This can be done in most cases by right-clicking the network icon in your computer’s notification area near the system clock, and selecting “Repair”.

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