Windows 7 / Networking

---

IPv6 addressing

As most administrators know, IPv6 is designed to increase the size of the IP address space, thus providing addresses for many more devices than IPv4. The 128-bit address size of IPv6 allows for 2128 possible addresses, an enormous number that works out to over 54 million addresses for each square meter of the Earth's surface.

In addition to providing more addresses, IPv6 will also reduce the size of the routing tables in the routers scattered around the Internet. This is because the size of the addresses provides for more than the two levels of subnetting currently possible with IPv4.

Introducing IPv6

IPv6 addresses are different from IPv4 addresses in many ways other than length. Instead of the four 8-bit decimal numbers separated by periods that IPv4 uses, IPv6 addresses use a notation called colon-hexadecimal format, which consists of eight 16-bit hexadecimal numbers, separated by colons, as follows:

xx:xx:xx:xx:xx:xx:xx:xx

Each X represents eight bits (or one byte), which in hexadecimal notation is represented by two characters, as in the following example:

21cd:0053:0000:0000:e8bb:04f2:003c:c394

CONTRACTING IPV6 ADDRESSES

When an IPv6 address has two or more consecutive 8-bit blocks of zeros, you can replace them with a double colon, as follows (but you can only use one double colon in any IPv6 address):

21cd:53::e8bb:04f2:003c:c394

You can also remove the leading zeros in any block where they appear, as follows:

21cd:53::e8bb:4f2:3c:c394

EXPRESSING IPV6 NETWORK ADDRESSES

There are no subnet masks in IPv6. Network addresses use the same slash notation as CIDR to identify the network bits. In the example specified here, the network address is notated as follows:

21cd:53::/64

This is the contracted form for the following network address:

21cd:0053:0000:0000/64