Hi-I take my laptop to the local library a lot. I've noticed that the IP address on their computers is the same as the one on my laptop. You have to be registered to use their computers (you use your library card) , & they "register" your laptop the first time you use it there. Well, does that mean the IP I get on both is my individual IP (under my name), or is the library's IP? Thanks for your help-I'm a liberal arts major-this is all a mystery to me!
That's the library's IP address and all of the computers there will most likely use that same 'external' IP.
Internally, each computer has their own IP. But since they all use the same external connection, they all get that same external IP.
Even being a Liberal Arts major, you should still take a computer class. 😀
It's something called Network Address Translation. There is actually one device with that IP. A router or (more likely) a firewall. That device, on the "edge" of the network, is running a special service that keeps track of who is doing what, and sends traffic back and forth from and to the device doing the actual traffic.
The how is pretty technical. Just think of it like an apartment building. Everyone in there uses the EXACT same address. No suite or apartment numbers. Just something like "123 Main Street." When a resident sends mail, he writes a note to himself which resident sent it, and if a reply comes back, the note tells him where the reply goes.
If mail comes in as a new message, he has to have special instructions. Apartment 12D always gets the Comcast mail. 6F gets all the Gas Company stuff.
That's the (very rough) illustration of what happens, and why your laptop and library PC both have the same IP when you come here.