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TCP/IP currently has a limit of 4 billion IP addresses, and that's not enough. IPv6 blows away this limitation.
I have a new notebook with Windows Vista Home Premium installed. I noticed when I view Network Properties, I see that Internet Protocol Version 6 (TCP/IP v6) has been selected as well as TCP/IP v4. What is TCP/IP v6? Do I need it to search the web?
You don't need it yet, but someday you will. How soon? Good question.
Because 4 billion isn't a big enough number.
IP, or "Internet Protocol", is best recognized by the way it assigns "IP addresses" to devices on the internet. An IP version 4 address, the current common technology, is a 32 bit number, represented by 4 numbers separated by periods. 126.96.36.199 is an example of an IP address (this one, assigned to the domain microsoft.com).
A 32 bit number can represent up to 4 billion different IP addresses. In reality the number is somewhat less, since some numbers and digits have reserved meanings.
As it turns out, 4 billion isn't enough. Because of the way that IP addresses are assigned and used, I've heard we may "run out" of IP addresses in several years.
Enter IP version 6, or IPv6. IP version 6 introduces many additional features, but the most notable one is that an IPv6 address is 128 bits long instead of 32. While that seems like it's only 4 times larger, it's not. It represents 3.4×1038 different IP addresses.
Put another way:
IPv4: 4,294,967,296 addresses
IPv6: 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses.
(That's 4 billion times 4 billion times 4 billion times 4 billion - where "4 billion" is in computer terms using powers of 2, or 4,294,967,296.)
When you start seeing them, you'll see IPv6 addresses as groups of 4 hexadecimal digits separated by colons. 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 is a valid IPv6 address. It turns out they've also created some shorthand so all IPv6 addresses, while still 128 bits in length, may not be represented by a string quite that long.
We're not likely to run out of IPv6 addresses any time soon.
Will you be forced to switch? Someday, maybe. The good news is that for now it's pretty transparent, and you probably won't be affected for some time. There actually is some IPv6 traffic on the internet already, using techniques to coexist with the IPv4 traffic.
The fact that you're seeing an IPv6 protocol available within Windows is actually good news, because it means that one major part of the infrastructure of the internet - millions and millions of Windows based PCs - are ready to go.
But for now, I'd just leave it enabled and otherwise ignore it.
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