IPv6 Addressing Scheme - Bigger is Better
One of the main reasons for needed a new version of IP is the address scheme seen on the last page. IPv6 handles this with a 'bigger is better' method - it simply lengthens the field that contains the address. The IPv4 address field has 32 bits, broken into the classes as shown in the previous section. The new IPv6 address field is comprised of 128 bits, which allows for a large, large number of addresses. How large? Large. The number of addresses is equivalent to 655368, which is 340,282,366,920,938,463,463,374,607,431,768,211,456 , or about 340 undecillon. The format of the address field in IPv6is as follows:
The 64 bit host address portion is usually generated from the computer's mac address on the network card, which is unique to each network card. This addressing scheme allows for such a large number that even thinking about it is unfathomable. The number of addresses if layed out uniformly on the surface of the earth would be about 7x1023 per square meter. This may seem like overkill, but there is still a division of these addresses, similar to the 4 classes in IPv4, just a lot more classes. The classes are based off a prefix, once again similar to IPv4, but they are mostly unassigned at the moment since demand isn't there. Another important item regarding IPv6 is that it does take into account that IPv4 addresses will still be on the net, and is able to use a prefix to create a class for this. The example below shows how a current IPv4 class C address maps into an IPv6 address.
You will notice that the address can take a few different forms. The main thing to notice is that the zeros can be truncated, which is true with leading or trailing zeros, but not both. The way this is signified is by the '::' in the address. IPv6 figures out how many zeros to insert based off of the numerical values before and after it. An address that is 1234:5678:0000:0000:0000:0000:0000:0000 can be changed to 1234:5678:: (this is to show how trailing truncation works). An address that is 0000:0000:0000:ABCD:EF01:2345:0000:0000 could be ::ABCD:EF01:2345:0000:0000 or 0000:0000:0000:ABCD:EF01:2345::, but not ::ABCD:EF01:2345:: since it would be impossible to tell where the leading and trailing zeros go in what quantity.
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