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IPv6 Address Size and Address Space
(Page 2 of 3)
IPv6 Address Space
The 128 bits of IPv6 addresses mean
the size of the IPv6 address space is, quite literally, astronomical;
like the numbers that describe the number of stars in a galaxy or the
distance to the furthest pulsars, the number of addresses that can be
supported in IPv6 is mind-boggling. See Figure 94
for an idea of what I mean by astronomical.
Figure 94: A (Poor) Representation of Relative IPv4 and IPv6 Address Space Sizes
I wanted to make a cool graphic to show the relative sizes of the IPv4 and IPv6 address spaces. You know, where Id show the IPv6 address space as a big box and the IPv4 address space as a tiny one. The problem is that the IPv6 address space is so much larger than the IPv4 space that there is no way to show it to scale! To make this diagram to scale, imagine the IPv4 address space is the 1.6-inch square above. In that case, the IPv6 address space would be represented by a square the size of the solar system. J
Since IPv6 addresses are
128 bits long, the theoretical address space if all addresses were used
is 2128 addresses. This number, when expanded out, is 340,282,366,920,938,463,463,374,607,431,768,211,456,
which is normally expressed in scientific notation as about 3.4*1038
addresses. That's about 340 trillion, trillion, trillion
addresses. As I said, it's pretty hard to grasp just how large this
number is. Consider:
- It's enough addresses for many trillions of addresses
to be assigned to every human being on the planet.
- The earth is about 4.5 billion years old. If
we had been assigning IPv6 addresses at a rate of 1 billion per second
since the earth was formed, we would have by now used up less than one
trillionth of the address space.
- The earth's surface area is about 510 trillion
square meters. If a typical computer has a footprint of about a tenth
of a square meter, we would have to stack computers 10 billion high
blanketing the entire surface of the earth to use up that same trillionth
of the address space.
Okay, I think you get the idea. It's
clear that one goal of the decision to go to 128-bit addresses is to
make sure that we will never run out of address space again, and it
seems quite likely that this will be the case.
Key Concept: The IPv6 address space is really, really big. J
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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