How to locate geographically a dynamic IP address?

I am managing a forum where it collects IP addresses of each user on each post. The issue is that I suspect that several of them are using multiple user id's but while some can be uncovered through their static IP address, others are using dynamic ones, such as I found that there are several excellent IP locators which can identify even the city of the IP address, but when it's like this one then I couldn't find any viable alternative.

Thanks for any suggestions!
Nicola SiottoDirectorAsked:
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Unfortunately in a lot of cases the closest you will be able to track down a dynamic IP address is the country to which the IP comes from. This is because these IP to location finding tools use information from the WHOIS (published by the registry controlling the IP range - RIPE is an example) to find out the address of the owner of that IP.

For that address to be the exact location of where that IP is located, the person / company which is using the IP must be pretty large. In most cases, it would be the address of the ISP (since ISPs own most of the addresses on the Internet), and as such, it would be the ISP's headquarters which you are pulling up the city for. This also applies to many static IP addresses - I've just checked and my static addresses at work are showing the ISP's location, many hundreds of miles away from here.

Nicola SiottoDirectorAuthor Commented:
This is also my doubt but worth trying to get some further idea or suggestion in this respect.

As I said, the only way you are able to track down an IP to its exact geographic location is if the person who uses that IP has registered their address in the IP registry's WHOIS. RIPE, AfriNIC, APNIC, ARIN and LACNIC are the 5 registries which handle IP address allocation for various regions of the world, with the allocations being assigned by IANA (listed in

The IP to address finder uses the address an ISP has registered to locate an IP to tis geographical location. It's impossible for you to track dynamic IPs to the customer of an ISP who it is allocated to using these services - the ISP are not going to update the WHOIS at the appropriate IP registry every time the dynamic IP is reallocated to a new customer (it would be too much of an administrative nightmare), and plus by the time you are able to do the lookup, it is likely the person who was using that dynamic IP had already disconnected or had a new IP address assigned, and thus your information would be totally inaccurate.

Sorry, but this is one of those where the answer is "You can't do that".


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Nicola SiottoDirectorAuthor Commented:
Well it's not the answer that I expected and it does not solve my problem but I believe for your effort it is fair to assign the score to you. Thanks!
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