Getting ready for IPv6
Sean Walton

The new revised protocol of IPv6 is going to provide some new advantages and features. This tip from InformIT takes a quick look at some of the differences.

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Widening the Network with IPv6

A worldwide network has to be flexible enough to support disparate addressing, subranges for local networks, and enough breathing room for billions more computers. The Next Generation of IP, Ipng or IPv6, defines an address that's four times the size of IPv4--16 bytes instead of 4 bytes. It also sets aside several ranges for multicasting and foreign network addressing.

IPv6's 16-byte address can handle about 3.4x1038, which when compared to IPv4's address space, appears to give you as the programmer and/or administrator unlimited flexibility. The allocation of IPv6's addresses will continue the same approach as now done, allocating address blocks to groups. This means that we can expect many years of longevity.

Naturally, several things had to change to support the new protocol--not the least of which is the IP packet. The IP packet, the most fundamental block of data that a program can work with, must carry at least the destination address, the source address, and the length in bytes. The new protocol simplifies the packet and reduces the overhead load.

Actually, the IPv6 header is twice the size of the IPv4 header (40 bytes versus 20 bytes). However, the IPv6 format packet no longer counts the header as part of the packet size. IPv4 never could give a full 65535 bytes, because the header used 20?60 bytes of that space. The IPv6 header is "fixed" at 40 bytes, and the data can be as large as 65536 bytes--or even larger.

IPv6 takes advantage of the newer, super-high-bandwidth networks (greater than 1 gigabyte), by supporting jumbograms. The current IPv4 packet can't handle any packet bigger than 65535 bytes. On newer, faster networks, that limitation is very constricting and is prone to fragment the network (especially Ethernet). IPv6 offers a jumbo payload that allows packet sizes up to 4 gigabytes!

The representation had to change as well. To distinguish the familiar IPv4 dot notation (and perhaps to increase readability a little), the new protocol uses eight 16-bit hexadecimal numbers separated by colons. For example, you may get an address like this:

2FFF:80:0:0:0:0:32C:2356

or

2FFF:80::32C:2356

The two colons are shorthand for all zeros in the second example. You can even represent an IPv4 address using this:

0:0:0:0:0:FFFF:XXXX:XXXX

or

::FFFF:XXXX:XXXX

where XXXX:XXXX is the IPv4 address expressed as hexadecimal. As you can see, the new protocol really does encompass the old. The benefits of moving to IPv6 include better addressing, better multicasting (covered in my earlier articles), larger-capacity messaging, and multi-networks. But before you can actually use it, you need support for it.


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Related Book

Implementing IPv6, 2nd Edition
Author : Mark A. Miller and P. E. Miller
Publisher : Hungry Minds
Published : Jan 2000
Summary :
If you are a network manager transitioning from an older Internet Protocol to Internet Protocol version 6, you know that version 6 includes enhancements to maintain the network efficiency required by increasing traffic.


This was first published in July 2001

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