Addresses

IPv4 used four octets of dotted decimal notation. The binary address was broken up into four groups and translated into decimal, to make one of the most confusing schemes in history!

The ATU Letterkenny web server was at 193.1.80.100

IPv6 uses eight groups of sixteen-bit words, for example 2001:0770:003c:1710:0000:0000:0000:0001

n IPv6, the representation is in hexadecimal, so it is a bit more logical, but the size of the address space makes things look daunting.

Zeros can be collapsed, we call that to elide.

The rules are; if there are a string of zeros, you can remove them once. If there are two strings of zeros, you can’t remove then both, otherwise there is no way of knowing where the bits in the middle are! If you have four zeros, you can just use one and leading zeros can also be removed. The address above becomes 2001:770:3c:1710::1

The loopback Interface is;

• IPv4 = 127.0.0.1/32

• IPv6 = ::1/128

The prefix is the part of the address that indicates the bits that have fixed values or are the bits of the network identifier and we do not use subnet masks. Prefixes for IPv6 routes and subnet identifiers 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.

The original model was very simple; the first 64 bits are the network; the next 64 bits are the node. But the first 64 bits can be divided into different prefix lengths for efficient routing.

21da:a3::/48 is a route prefix

21da:a3:0:2f3b::/64 is a subnet prefix