Find all computers using the same public IP

Question

I noticed frequently that some site say that I already visited it... Or that I am currently online, or some other strange stuff like that...

I guess that someone is also using the same internet IP as my network, or someone is on my network... How I check all computers using that same IP? (or computers on my network... or... you get it :P)

EDIT: Clarifications: I know the internet IP is random, what I mean is that those "sharing" sites for example (like rapidshare, megaupload, whatever...) may say that my IP is already downloading something. Or when connecting to a IRC network, it may block my connection saying that I am a "clone" (the term some IRC networks use for someone connecting several times).

My network structure: There are a radio antenna that grabs the internet from the ISP, they don't allow me to fiddle with the modem... Then a router distributes the internet using both wireless and cables. I guess either the ISP is sharing that IP with several people, or someone is tapping on the wireless.

Answer 1

Depends on what kind of connection you have.

If it is a network through a known shared connection, like in a dorm or at an office, you would need to go through your admin.

If it is a home network with wifi, you can go to the router's administration settings to see active connections.

Bear in mind that a lot of ISP's supply DYNAMIC IP addresses, which means they really own a range of IPs they assign dynamically to their customers. It is entirely possible that you got the IP address someone else had before.

Answer 2

It sounds like you are using a shady ISP that is sharing the same WAN IP for all the wireless modems in your area which would cause the problems you described. If not, then 1) someone is connected to your home network and you should make sure your wifi is secured or 2) if you frequently turn your modem or router off than you might be leasing a dynamic IP that was just recently released by another customer of your ISP, keeping them on all the time will eventually solve that issue.

Answer 3

Are you trying to find out which computers have the same external IP address as you?

If so, you will need access to the router/gateway on your network to see who is using that router/gateway.

If you don't have access to it, you can use nmap to scan your local subnet, that will give you an indication of who is using the same external ip address as you, but won't be entirely accurate.

You need to describe you network a more clearly.