IPv6 Address Structure
IPv6 addresses are 128 bits in length. They are made up of eight 16 bit blocks separated by colons. Each block contains a 16 bit case sensitive hexadecimal value.
For example x:x:x:x:x:x:x:x where”x” is equal to 16 bits.
Leading zeros.
Leading zeros in an IPv6 address are optional. For example an IP address of 2001:db8:31:0:0:0:0:1 can also be written as 2001:db80:31::1 the missing zeros are calculated to make the address 128 bits. In this case it is clear that four zeros were removed. This process is called zero compression. Successive fields of zeros are allowed, but only one time in an address.
Loopback Address.
Similar to IPv4’s 127.0.0.1, Ipv6 has its own loop back address. The loopback in Ipv6 is 0:0:0:0:0:0:0:1 or can also be zero compressed to ::1. This address is also used for troubleshooting a network.
Prefixing.
Within the Ipv6 protocol there is a similar notation to a forward slash net mask prefix in IPv4. The prefix notation in IPv6 determines how many left most bits are assigned by authority and how many bits are assigned locally, or how many bits of the address specify the prefix.
Aggregatable global.
Aggregatable global unicast addresses are similar to the IPv4 public addresses and can be routed over an IPv6 Internet. The format prefixes of these addresses are 001::/3. These addresses were designed to support efficient hierarchical addressing and routing. The unique scope of this address scheme is the Internet itself. The lower 3 bits are used to identify the address as globally unique. The next 45 bits are allocated by the ISP of the host, this makes up a prefix of ::/48. The following higher 16 bits determine site topology (subnet) on which the host belongs to. The remaining 64 bits are the unique interface identifier made up of the MAC address and subnet of which it’s on.
To create the EUI a device’s MAC address is used. The value “fffe” is inserted into the middle of the 48 bit MAC address therefore making it 64 bits. This also means that it becomes a unique identifier for that machine. A MAC address is a global unique identifier for networked machines. For security reasons RFC 3041 states that a networked machine can also generate random identifiers that only last a few hours, this means long term tracking of computers would be a lot more difficult.
