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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)
                9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)
                     9  IPv6 Addressing

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IPv6 Addressing Overview: Addressing Model and Address Types
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IPv6 Address and Address Notation and Prefix Representation
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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 I’d 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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IPv6 Addressing Overview: Addressing Model and Address Types
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IPv6 Address and Address Notation and Prefix Representation
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Version 3.0 - Version Date: September 20, 2005

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