IPv6 Basic

The Internet is running out of Internet Protocol Version 4 (IPv4) addresses. In 1998, the Internet Engineering Task Force (IETF), a standards body, created Internet Protocol Version 6 (IPv6) as a replacement to IPv4 with the goal to increase the Internet's address space. However, IPv6 also has some enhancements, including autoconfiguration, easier network renumbering and built-in security through the IPsec protocol. Transitioning to IPv6 enables the Internet to continue to grow and enables new, innovative services to be developed because more devices can connect to the Internet.

In contrast to IPv4, which defined an IP address as a 32-bit value, IPv6 addresses have a size of 128 bits. Therefore, IPv6 expands the number of available addresses (about 4 billion addresses as in IPv4)to 340 trillion trillion trillion (or, 340,000,000,000,000,000,000,000,000,000,000,000,000) addresses. With this number of available addresses, it will be able to accommodate devices that are online today and those that may be in the future. These may includes TVs, fridges, computers, phones and so on.

Many major websites and Internet Service Providers now support IPv6, but there are still many more who need to switch.

IPv6 Address representation

IPv6 addresses in long form are represented as eight sets of four hexadecimal digits separated by colons, but that makes for long addresses. Here is an example below:

2001:0db8:0000:0000:0000:0000:0002

The address above is using the hexadecimal colon notation. Every two bytes are written in hexa format with a colon separating them.

IPv6 addresses can be written in short hand using two conventions:

1. Zero Suppression
- all IPv6 address segments are 16 bits
- The leading zeroes in each segment can be left out of the address segment.

2. Zero Compression
- Since all addresses contain 8 segments, following sections of zeroes can be collapsed to a double colon.
- However this double colon can appear only once in the address representation.

Using these two rules, our example IPv6 address 2001:0db8:0000:0000:0000:0000:0002 collapses to 2001:db8::2.

IPv6 Prefix numbers

Prefixes for IPv6 subnet identifiers and routes are expressed in the same way as Classless Inter-Domain Routing (CIDR) notation for IPv4. An IPv6 prefix is written in address/prefix-length notation.

For example:

805B:2D9D:DC28::/48

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

In the above example the first 48 bits of the address represents the main prefix or network ID and the last 80 bits are used for individual host ID. The prefix notation will be found in routing tables and used to express main networks or subnets.

IPv6 Address Categories

Three categories of IP addresses are supported in IPv6:

Unicast Addresses: Unicast addresses assigned to hosts and router interfaces. Packets destined to unicast address are delivered to a single interface.

Multicast Addresses: These are addresses that represent various groups of IP devices. A packet sent to a multicast address is delivered to all interfaces identified by that address.

Anycast Addresses: Anycast addresse identifies multiple interfaces. A packet sent to an anycast address is delivered to the closest member of a group, according to the routing protocols' measure of distance. Anycast addressing is used when a message must be sent to any member of a group, but does not need to be sent to them all.

There are no broadcast addresses in IPv6. All broadcast types of IPv4 are performed using multicast address type of IPv6.