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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

IPv6 Addressing Overview: Addressing Model and Address Types 1 2 3 IPv6 Address and Address Notation and Prefix Representation

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”.

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.

IPv6 Addressing Overview: Addressing Model and Address Types 1 2 3 IPv6 Address and Address Notation and Prefix Representation