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I was wondering how easy it is to trace this back to the actual connection (house). Is it possible since it is dynamic and changes each time the modem is restarted? Does it make the task more difficult if the user is using a cable modem?

Thanks

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You would probably need a subpoena from the ISP (at least that is how I think you do it in the US). –  Zifre Jul 21 '10 at 0:17
    
I don't think that cable modem is making it any more difficult. And remember, modem's MAC can be traced too! And it's unique to the device. –  AndrejaKo Jul 21 '10 at 0:36
    
@AndrejaKo - "modem's MAC" ? no such thing. The MAC address belongs to the ISP's device (serial multiplexer or integrated modem bank) not your home's modem. From the ISP's perspective the modems act like a long (dumb) piece of wire. –  hotei Jul 26 '10 at 23:56
    
just to clarify, I'm speaking about phone modem, not cable modem when I say no MAC. On re-reading, I think AndrejaKo may have swapped subjects in that sentence, so I think we agree, just said it differently. –  hotei Jul 27 '10 at 0:10
    
@hotei Yes, I was thinking about cable modems at the time (OP mentioned cable modems). As far as I know classic fax modems don't have MAC address. Also MAC addresses for ADSL and similar modems which use Ethernet to router would only have MAC address for ports on internal side. It should be invisible from the ISP side, right?? –  AndrejaKo Jul 27 '10 at 1:25

2 Answers 2

In a word... Very. The ISP probably keeps a log of the MAC address (of the modem or router) the IP and the time. All it takes is a database query to find the info... and a subpoena to get the ISP to run the query. :-)

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Modem's don't have MACs. What they do have that identifies them is telephone numbers and those get logged. You can get around this but it's not trivial and LEOs have a lot of practice finding folks that try. –  hotei Jul 27 '10 at 0:00
    
I meant cable modem since the question had to do with dynamic IPs and I presumed High Speed internet. Phone modems have phone numbers via caller ID (which likely are not logged) but more importantly user ID and password authentication which is. –  Chris Nava Jul 27 '10 at 5:03

As people said, it should not be possible except in law enforcement. However, you can get a rough estimate where the IP is coming from using services like http://www.ip2location.com. It is not always accurate and precision can vary quite a bit, though.

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