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I'm encountering some IP strangeness today and hoping to find an explanation.

In short, I'm based in Seattle, WA with my ISP being Comcast. While browsing Facebook's account settings, I noticed that my active session was located to Mount Laurel, NJ.

At that point I ran a search in Google for 'my public IP', which returned an interesting result: a string of characters in the following format:

2601:8:b000:xxx:xxxx:xxxx:xxxx:xxxx

Normally, a search for my IP returns something like:

67.xxx.xx.xxx

A phone call to Comcast got me nowhere, but using Comcast's phone-menu debugging tools, I was able to send a 'refresh signal' to my modem. After that, the search for 'my public IP' yielded the expected result... for about 5 minutes, and then it returned to the new string of characters.

Does anyone know of an explanation for this?

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3  
That looks like an IPv6 address... –  nhinkle Nov 8 '13 at 20:54

2 Answers 2

up vote 5 down vote accepted

If you click the "Learn More" link that shows up when you Google for your IP, it explains what you're seeing:

IP addresses are sequences of numbers that are usually displayed in readable notations, such as 172.16.254.1 (for IPv4) and 2001:db8:0:1234:0:567:8:1 (for IPv6).

Comcast has both IPv6 and IPv4 enabled for many of their regions.

For more info on that, you can visit their IPv6 Information Center: http://www.comcast6.net/

Most recent entry there:

Published on Friday, September 20, 2013
Residential native dual stack has been launched to Comcast customers across Washington state!

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Wow, the first post on that page is very relevant. It's posted Sept. 20 and mentions the launch of IPv6 across WA state. This accounts for my not seeing the alternate IP in the past. Thanks for the link. –  Stuart Kershaw Nov 8 '13 at 21:14

That is your IPv6 address. Your 67. number is your IPv4 address.

From a command prompt, type:

ipconfig /all

and you will see both

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2  
If they have a router, then they will see a different set of IP addresses. –  daxlerod Nov 8 '13 at 20:58
2  
The set of IPv6 adresses that start with 2601:: are registered to Comcast in Mt. Laurel, NJ. whois.arin.net/rest/net/NET6-2601-1/pft –  daxlerod Nov 8 '13 at 20:59
    
Interesting, I've not seen the IPv6 address displayed before, and I've certainly not had my location traced to Mount Laurel, NJ during an active session. Would there be any reason for the IPv6 address to begin returning in searches and on FB? *Note that this occurs from any device on the network. –  Stuart Kershaw Nov 8 '13 at 20:59
    
Note that Mt. Laurel is in Burlington county NJ, approx 15 mins outside of Philadelphia, Comcast corp headquarters. They have a lot of equipment in Camden and Burlington counties. –  horatio Nov 8 '13 at 21:16
    
@daxelrod: The IPv6 address should be the same whether they have a router or not. IPv4 addresses are normally those of the router (NAT device). If IPv6 privacy is enabled, the IPv6 address will change over time. –  BillThor Nov 8 '13 at 21:42

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