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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 Address Size and Address Space 1 2 3 4 IPv6 Address Space Allocation

IPv6 Address Hexadecimal Notation

To make addresses shorter, the decision was made in IPv6 to change the primary method of expressing addresses to use hexadecimal instead of decimal. The advantage of this is that it requires fewer characters to represent an address, and that converting from hex to binary and back again is much easier than converting from binary to decimal or vice-versa. The disadvantage is that many people, even computer people, find hexadecimal difficult to comprehend and work with, especially because the notion of 16 values in each digit is a bit strange. (I'm not one of them, but then I'm a geek.)

The hexadecimal notation used for IPv6 addresses is similar to the same method used for IEEE 802 MAC addresses, for technologies like Ethernet. There, 48 bits are represented by six octets, each octet being a hexadecimal number from 0 to FF, separated by a dash or colon, like this:

0A-A7-94-07-CB-D0

Since IPv6 addresses are larger, they are instead grouped into eight 16-bit words, separated by colons, to create what is sometimes called colon hexadecimal notation, again shown in Figure 95. So, the IPv6 address given in the example above would be expressed as:

805B:2D9D:DC28:0000:0000:FC57:D4C8:1FFF

To keep size down, leading zeroes can be suppressed in the notation, so we can immediately reduce this to:

805B:2D9D:DC28:0:0:FC57:D4C8:1FFF

Hmm. Well, it's definitely shorter than dotted decimal, but still not much fun to look at. When you are dealing with numbers this big, there's only so much you can do. This is part of why under IPv6, use of DNS names for hosts becomes much more important than it is in IPv4; who could remember a hex address that long?!

IPv6 Address Size and Address Space 1 2 3 4 IPv6 Address Space Allocation