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Is it possible to find out what IP addresses a computer has been assigned by their ISP in, say - the last six months? I know the current IP address but would like to see the one before that, and the one before that one, etc.. I'd like to eliminate IP addresses from web logs that are mine for at least 6 months.

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up vote 5 down vote accepted

Depending on how you send e-mail, your current IP (at that time) might be present in the Received: header of mails other people got from you.

Try and send an e-mail to yourself and look at its source code (how to do that depends on how you access your mail) and compare the addresses that show up in the various Received: headers to see whether your current address appears there.

If it does, you “just” have to somehow get one of the e-mails you sent at the time you’re interested in. You might have sent one to a friend or to a mailing list.

(Yes, the chances to find the IP this way are pretty low, but depending on how important it is to find it out it might be worth the effort.)

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Yes! Thank you! This is excellent. – SmartMethod Aug 27 '10 at 1:24

Your modem/router might keep logs on which IP the DSL was registered to. Usually the modem's logs/UI is accessible by navigating to its IP through your browser.

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I will check the log files, that is a good place to start. Thanks! – SmartMethod Aug 12 '10 at 15:24
Good start but the log file doesnt go back but 5 days on my router. :-( Any other log somewhere else on the PC maybe? – SmartMethod Aug 12 '10 at 15:31
Maybe there are some webpages that you use frequently that track your IP? Gmail tracks IP, but only for the past 24 hours. – Jarvin Aug 12 '10 at 15:37
@Optimal Your PC doesn't register your external IP addresses... if it's not in your modem, you probably wont find another log that goes back 6 months. – BloodPhilia Aug 12 '10 at 15:38
If you were to call your ISP they should have records but the odds of them actually providing it to you are slim-to-none. – Shinrai Aug 12 '10 at 16:01

If you use GMail or Yahoo you can log on and look at the headers in your Sent folders. GMail keeps them forever (unless you delete them).

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Also in Gmail, at the bottom right is a link to your account activity.

Clicking it will show information, including the accessing IP address, about the last 10 Gmail sessions: Gmail Account Acvitity

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