So what's this IP Version 6 stuff ?

When IPv6 was in its early stages, one of the main topics of the discussion was how long the IPv6 address should be. The IPv4 address is 32-bit, with a theoretical maximum of over four billion addresses. The hierarchy of the IPv4 address, i.e. network, subnet and host, reduces the actual amount of addresses available. IPv6 addresses, being 128 bits long, need 32 characters to write in the general case, if standard hex representation, is used, plus more for any punctuation inserted (typically about another 7 characters, or 39 characters total).

1080:0:0:0:8:800:200C:417A

In decimal, considered as a 128 bit number, that is 21932261930451111902915077091070067066.

It is always necessary to be able to write in characters the form of an address, though in actual use it is always carried in binary. For IP version 4 (IP Classic) the well known dotted quad format is used. That is, 10.1.0.23 is one such address. Each decimal integer represents a one octet of the 4 octet address, and consequently has a value between 0 and 255 (inclusive). The written length of the address varies between 7 and 15 bytes.

For IPv6 however, addresses are 16 octets long [IPv6], if the old standard form were to be used, addresses would be anywhere between 31 and 63 bytes, which is, of course, untenable.

Because of that, IPv6 had chosen to represent addresses using hex digits, and use only half as many punctuation characters, which will mean addresses of between 15 and 39 bytes, which is still quite long. Further, in an attempt to save more bytes, a special format was invented, in which a single run of zero octets can be dropped, the two adjacent punctuation characters indicate this has happened, the number of missing zeroes can be deduced from the fixed size of the address.

Introduction IP version 6 (IPv6) is a new version of the Internet Protocol, designed as the successor to IP version 4 (IPv4) [RFC-791]. The changes from IPv4 to IPv6 fall primarily into the following categories:

o Expanded Addressing Capabilities

IPv6 increases the IP address size from 32 bits to 128 bits, to support more levels of addressing hierarchy, a much greater number of addressable nodes, and simpler auto-configuration of addresses. The scalability of multicast routing is improved by adding a "scope" field to multicast addresses. And a new type of address called an "anycast address" is defined, used to send a packet to any one of a group of nodes.

o Header Format Simplification

Some IPv4 header fields have been dropped or made optional, to reduce the common-case processing cost of packet handling and to limit the bandwidth cost of the IPv6 header.

o Improved Support for Extensions and Options

Changes in the way IP header options are encoded allows for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing new options in the future.

o Flow Labeling Capability

A new capability is added to enable the labeling of packets belonging to particular traffic "flows" for which the sender requests special handling, such as non-default quality of service or "real-time" service.

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