Is our IP address always the same?

What former dynamic IP address is now static?

• I used to have an IP address until about a year ago. I believe this was dynamic, as my ISP would charge extra for static IP, and you would have to ask for one. I recently found the "nnumber" of my old IP which was stored on my computer, in a document. Out of curiosity I plotted the old IP-address into "http://whatismyipaddress.com", and there it said that the IP address is Static.   So I wonder what happened. Is it just that someone new are using my old IP-address, and that they have now set it up as a Static address? (It is the same ISP that provides the IP address now as it was a year ago) It doesn't mean that the IP address was Static when I had it? And if I have understood it correctly, I would have to manually set up a static IP address on my router/modem? And since I haven't done that, it can't be that the IP address was Static when I had it? :)

• Answer:

  First, it's somewhat difficult to believe that someone's tool is going to actually capture every ISPs address allocation policies.  How do they know what's static and what's dynamic? Second, an ISP is free to use the address either statically or dynamically, and it is free to change that policy for a given address over time.  It may well have been dynamically assigned to you at one point and then reallocated for static addressing. Third, there's nothing that says that you can't continue to use DHCP to serve a statically assigned address.  The ISP can simply encode the information in their DHCP server.  In many ways, this is the most logical way of doing things, as it decreases subscriber overhead and support calls.