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Google says my IP address is something like this (I've changed it just in case there is anything personally identifiable in it).

Your public IP address is 2602:306:78c5:6a40:421e:6813:d55:ce7f

The above number (similar to the one Google gives me) translates to this integer:

50521109793518520187427681667365850751

(see http://www.webdnstools.com/dnstools/ipcalc for the best IP calculator I've found.)

My actual IP address, found at http://www.whatismyip.com, is something like this (again I've changed it a bit):

108.88.1009.77

Which is this integer:

1817734477

The Google IPv6 address isn't even in the IPv4 range. And why would Google say that is my address while WhatIsMyIP shows the seemingly correct IP?

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2 Answers

up vote 3 down vote accepted

Those addresses are both allocated to AT&T. Your ISP provides both IPv4 and IPv6 service, and you're using IPv6 to reach Google.

Both answers are "correct".

If you search for "my ip" on http://ipv4.google.com/, it should display your IPv4 address instead.

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Great answer. How did you know that? –  Buttle Butkus May 29 '13 at 23:15
    
And, if you know this, how/why would I be using IPv6 to reach some sites and IPv4 to reach others? I could perhaps ask that as a new question but I don't know if it would be right for webapps.stackexchange. –  Buttle Butkus May 29 '13 at 23:17
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Responding to the second question.

IPV4 is out of address space in some areas of the world, and nearly out elsewhere. ISPs are slowly turning on IPV6 for their customers. Fir a while you get both addresses (dual stack). IPV6 addresses look like 1234:5678:90ab:cdef:1234:5678:90ab:cdef and ipv4 addresses look like 123.234.123.234. The ISP that any address is allocated to can be looked up on the web.

Some web sites are IPV4 only, some are IPV6 / IPV4 dual stack, and a very few are IPV6 only. If your computer is dual stack and your ISP has turned on IPV6 and you have a relatively recent browser, the browser will pick the address that returns the fastest result for the first packet (happy eyeballs). If you have a somewhat older browser, it will prefer IPV6 even if it takes much longer.

So, if the web site supports IPV4 only, you will always access it over IPV4. If it supports IPV4 and IPV6, you will sometimes use one, and sometimes use the other. If it is IPV6 only, you will always use IPV6.

If you or your ISP onloy supports IPV4, then you will not be able to see IPV6 only web sites at all.

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