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I am an admin of an immigration forum. Security is my job One and protecting our members's info is my highest priority. Recently, I discover that there are 3 members who have posted from the same IP addresse and the same iPhone browser info. My questions,

  1. Is it possible that different people would have the same IP address for their iPhones?
  2. Can different people have the same iPhone plan would have the same IP address?
  3. I can find out the location of an IP address of the iPhone, but does that mean the owner resides at that location?
  • Are these posted within few minutes of each other? Or are they hours or days apart? – Question Overflow Jun 2 '14 at 2:25
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They could be using a network carrier which does not assign an unique IP address to each user but instead has only one external IP and uses Network Address Translation to allow multiple users to browse the web with that address. Such providers are quite rare in North America and Europe, but more common in other parts of the world.

There are countries where iPhones are sold exclusively with a plan by a single carrier. In that case all iPhone users from that country would have the same ISP and when that ISP uses NAT, also the same IP address.

In that case, a geoIP database would give you the location of their provider. These databases have very varying accuracy anyway. For my current IP address, all databases I tried return just the city I live in, which has a population of over a million.

Another explanation for multiple users sharing the same IP could be that they are using the same proxy server for anonymity. But having the same mobile phone and also using the same proxy service would be quite a coincidence.

bottom-line: There is a possibility that you are dealing with different people. However, it would be quite a coincidence. When you have other reason to believe that you are dealing with one user with multiple identities, it is quite likely to be the case.

  • +1, most mobile carriers in my country do CGNAT. (Though some use 1:1 NAT but the same address can still get reassigned to many people over a week.) – grawity Jun 1 '14 at 10:21

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