A question about IPs

Really, this is more just a verification of stuff I already (think I) know.

When two IPs (of different users) match, what does that mean?

If two users are using a fairly well-known proxy or web anonymizer, is it possible that the site/proxy could give out the same IP to both people (but at different times)?

It means that they’re coming from the same computer(or home network, if they’re behind a NAT firewall).

I would imagine that if two users used the same proxy they’d be almost guaranteed to get the same IP address.

So what are the chances that say, on my one board site, two people would have the same IP address? They still could be different people, right?

Thing is, my board is small. Only about 40 or 50 regular posters. What are the chances that two different people would have the same IP? I guess it is possible if they’re using the same proxy to surf by, but what are the chances of that?

If it’s two different people using the same computer, the chance is 100%

Haha, well I know thaaaaaaat. But these are two people who have always claimed to be two DIFFERENT people (and I’m pretty sure they’re different people) so how is it possible they’d have the same IP? And I’m talking exact match…no numbers are different.

ETA: They’re also two different people who have their location listed as being in different states.

Well this is kind of a key point that was left out of the OP. My girlfriend and I use different laptops but would have the same IP because I have internet service with a static IP at home.

Not if it’s a laptop used in different locations.

Yes. There are a couple of web based proxies that I use (never on the SDMB). I get the same exact IP address when I use them and anyone who used them would get the same IP as me.

Because they use the same ISP and the ISP gates their traffic out of the same box. The ISP can keep it straight using Network Address Translation, but you don’t have that option and so see those two different people as coming from the same computer. I don’t know if this is still true, but for a while all AOL users looked like they were in Georgia regardless of where in the country they actually lived because all AOL traffic entered the real Internet from machines in Georgia. Having some ungodly number of AOL users sharing the same IP address is hardly difficult to imagine.

So…I just to be clear…even though I have two people using a board (that has a very low membership) who are from different states, the odds that they would have the exact same IP addy is very good?

I wouldn’t say very good, but it is within the bounds of reason. It might be very good if they use the same ISP in the same region of the country.

Again, I have about 40 or 50 posters registered at my boards. Only about 20 or 25of them post daily, though. So, with knowing these numbers (I don’t know if that would change the odds or not) would you say that two of them having the exact same IP address is good odds?

Because it’s hard to read your answer here. Within the bounds of reason as in someday we may have another world war is within the bounds of reason or tomorrow your next-door neighbor may have breakfast bounds of reason?

Knowing what name the IP address resolved to would help. (A college address, generic ISP, proxy, etc.) Try one of the many online tools available. A quick Google search gives this useful site.

You aren’t going to get duplicate IP addresses with a modern service provider. The only reasonable scenarios I see are that they are behind the same NAT (in a house or office) or they happen to connect first to, say, a university machine and then head out to the web. How likely these are will depend on what your board is, what the users’ backgrounds are, etc. There’s no way to assign a probability in general. (A board about life at IBM might be more likely to have multiple people coming from a central machine. A board about mustard might be less likely.)

Can you provide more info (both about the board and its users and also about the IP address?)

The IP address in question is


Looks like we’re ok, Idle. I looked up the IP and it traces back to RIM – manufacturer of the Blackberry. The posters in question are posting via Blackberry.

Okay. :slight_smile: So you were right (in the PM–as were others in this topic).

Thank you.

I’ve seen two different users on this board who used the same proxy/anonymizer over two months apart and had the same four number match. And I KNOW they live 1000 miles apart and aren’t the same person.