On IP addresses - setting the record straight....

Given all the recent brouhaha over IP addresses, I thought it would be a good idea to help shed some light over these seemingly arcane numbers, and how they relate to our interactions over the internet. I do not claim to be an expert on these matters, however, I have worked in IT for a number of years, so I'd like to think that I have a wee bit more understanding about it than the layman. I am presenting this information as objectively as possible, without alluding to anyone else's concurring or dissenting views, and without necessarily taking sides. I always try to side with the truth, and if you're new here you merely have to glance up at the name of my blog to know that the search for the truth, among other things, is its reason for being. With that being said, here are some facts about IP addresses, in question and answer format:

What is an IP address?

An IP address (Internet Protocol address) is a unique number, similar in concept to a telephone number, used by network devices (routers, computers, time-servers, FAX machines, some telephones) attached to a network to refer to each other when sending information through a LAN (Local Area Network) or a WAN (Wide Area Network) or the Internet for example.

Reference: IP address: Wikipedia, the free encyclopedia

Do all individual computers have a unique IP address?

No. A computer directly connected to an internet backbone does have a unique IP address. Most of us however, aren't directly connected to an internet backbone. We typically access the internet via our respective Internet Service Providers or ISPs. Depending on the network architecture of our respective connections to our ISPs, we may either be allocated a unique (static) IP address which remains the same for our computer, a variable (dynamic) IP address which may change each time we log on, or just be referred to through our host's (ISP's) IP address.

Can two users have the same IP address?

Yes. As I mentioned above, a group of individual computers may all be referred to by a single IP address, if they access the internet via a single host. For example, xtnag, May and I, who all work in the same office, just appear to outsiders as a single IP address whenever we access the internet via our office computers. This is so because we share the IP address for our host (our office's proxy server) which is connected to our ISP.

What are the circumstances in which two people can have the same IP address?

Two users can share the same IP address if 1) they are accessing the internet via the same host (for example in an office setting, or an internet cafe); 2) they are using the same computer (obviously); 3) another user is mimicking the IP address of another, a technique known as IP spoofing.

So, how accurate is an IP address in serving as a personal identifier?

It depends. If a particular network allocates a static IP address to an individual computer, it is possible to identify it with a high degree of accuracy. On the other hand, if a network assigns a dynamic IP address, identifying a specific computer is only accurate for a single login session. Once the computer logs off and logs on again, the IP address is already different.

Also, if internet access resources are shared, multiple computers may be referred to only by a single IP address.

If a single computer has multiple users, this further complicates things.

In general, an IP address is accurate enough to pinpoint a user's geographic location, the ISP, perhaps even a city or a specific area. In reality however, it performs poorly as a personal identifier given the number of variables, except under the most ideal of conditions.

So what's the bottomline?

By itself, an IP address is not sufficient to prove beyond a shadow of a doubt that two individual users are in fact only one. In this regard it is only circumstantial, and corroborative at best, useful only if there are other pieces of evidence which point toward the same thing. I will refrain from venturing an opinion on matters in this regard, since that would be in the realm of speculation, more so considering that I do not know all of the material facts.

Hope some people find this useful.

Quaere Verum.

Postscript:

If there are mistakes in my technical analysis, please feel free to point them out, and I will correct them if so warranted.

Links:

IP Address as a personal identifier