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A question about IP addresses

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IamSmooth

Thu Dec 08 2011, 02:54PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

While I am a reasonable programmer, I know very little about the low level tech involved with the transfer of data across the internet. I know that my computer at home has an IP address. Is it possible to change this address. I want to "change" my identity so I site that I have visited does not think it is me. Is this possible without going to another location where I know the IP address is different?

Mads Barnkob

Thu Dec 08 2011, 03:25PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Your outgoing IP adress from your router, if you use DSL, is highest likely dynamic, that means you get a new IP assigned from your ISPs DHCP server every time you log onto their network.

Since a huge network like the internet is still maintained within the limits of 255^4 possible IP adresses and much less subnets, routers are used as gateways to separate the internet into many small networks connecting to a larger that connects to a giant network.

One of the few chances you have is to use proxy servers, there are a whole bunch of free ones you can find.

But its hard to advice without knowing the application... are you going to click your own banner commercials? Do you want to vote 5000 timer in a competition? etc.

IamSmooth

Thu Dec 08 2011, 03:34PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Your answer opens up a whole bunch of questions. I guess the best thing is to ask where can I read about this topic so I can get a really good understanding of it?

I don't wish to click my own ads, but I wouldn't mind knowing how to do it. If I were banned from a site I wouldn't mind knowing how to disguise myself. I just want to learn about this much like any other subject.

So, any good reference books?

Steve Conner

Thu Dec 08 2011, 07:06PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Reference books, lol. The technology changes so quickly, a book wouldn't be the best place to start. In the kinds of scenarios that Mads hints at, the authentication mechanism is most likely a cookie, or your account in the forum database, which is linked to a session cookie.

That's why most websites insist you create a user account and log in: they haven't a hope in hell of figuring out who you are otherwise, or even whose packets are whose, as HTTP is a stateless protocol. Once you have logged in, every HTTP request made by your browser is tagged with your session cookie, and the server can disentangle the hundreds of data streams coming at it from different users.

Tools like the famous Firesheep allow you to have fun viewing and hijacking other people's browser sessions, when run on an open wi-fi network. But this may be illegal in your country.

TCP/IP is an old enough technology that many good paper books are available. But an IP address is useless for identification, for the reasons given above: they are dynamic, and thanks to the wonders of NAT, several computers can share one from the Internet's point of view.

You can Google (or other search engine) any of the above and get lots of information. I've found the TCP/IP Guide

useful in the past, although as I said, it tells you nothing about how your identity is tracked online.

If you type "What is my IP" into Google, it will tell you. The answer very probably won't agree with the one given by your computer's network settings: this is an example of NAT.

AndrewM

Thu Dec 08 2011, 08:26PM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

Your question actually involves two separate ones - can you change your identity and can you change your apparent IP. As the others have mentioned, the IP is not a terribly good way to identify someone on the internet, however indeed people (and courts) do try. If indeed you're being tracked by IP and not cookie or MAC or whatever then I'll try to answer...

Changing your IP ("spoofing") is sometimes possible with effort, and sometimes intrinsically impossible.

Imagine a simple instant messaging protocol. When you type a message (say, "Hello world") your instant messaging client will pass that string, plus its intended destination (IP address and port) to whatever subsystem in your OS is responsible for facilitating TCP or UDP communications. In Windows, for example, requests from the instant messaging client would be sent to the "Winsock"/Windows Sockets API which is responsible for formatting packets and passing them on to the hardware stack.

The system takes your message "Hello World" and the destination and formats that information into a properly structured "packet" for the protocol in use (TCP or UDP). The packet consists of a header and a body (your message, in this case) - the header is generated automatically by the system to contain bunch of information but most importantly the source (your IP) and the destination. It is not straightforward to screw with this process since it happens at the Windows (or whatever) API level... but it can be done. However if you were to spoof the IP address in the packet header, the recipient would be unable to reply to you since the packet would no longer contain your reply-to address (the IP)! Ergo, generally speaking, you cannot count on being able to have spoofed your IP address AND have two-way communication. But if you're an evil mastermind and all you need is to send messages TO your botnet but not recieve them, this isn't much of a limitation.

However...

Even if you DID spoof your IP in this way, lets imagine you're behind a router in your home. When you attempt to send your packet out to the internet it gets stamped by your computer with your local IP address - thats an address only valid inside your home network. You can spoof that, but when the packet reaches your router, the router strips off your packet header and generates a new one based on the router's global IP. So your spoofing conceals which computer on your network originated the request, but the router undoes it once it leaves your home. Ergo if someone was tracing you they'd be lead right to your door (or internet account, really).

Also depending on your internet provider's configuration, they may repeat the same process - some ISPs (generally wireless ones) have you sitting behind a router which would undo your spoof even if you weren't behind a router in your home.

On top of that, its trivial for a good network manager to notice packets with spoofed IPs and disallow them.

A trusted proxy - that is, a system that will bounce your packets for you and promise to forget/not log where they came from, is really the only way.

IamSmooth

Thu Dec 08 2011, 08:29PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I think I have a lot to read. Speaking of cookies, I think I will get one to eat right now.

Do any of you know why they were called "cookies"?

Steve Conner

Thu Dec 08 2011, 08:51PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I have no idea. They were originally called "magic cookies" if that helps, and existed long before the Web.

Before that they were "magic numbers". http://en.wikipedia.org/wiki/Magic_number_(programming)

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