The computers in my office share the same IP address. Having that in mind, how does the Internet know that when I request a file from a remote server, it is exactly my computer that should receive the file and not one of the other computers (in my office) that share the same IP address?
closed as not a real question by dyasny, Ward, mdpc, MDMarra, Scott Pack Dec 17 '12 at 1:40
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.
It uses the tuple (source ip, source port, dest port, dest ip).
Therefore it does not identify a computer but a connection and that is all that matters from an Internet-server point of view.
You router then has a table that allows him to know to which computer he needs to forward the connection. This is called NAT.