Even as NAT ( Network Address Translation ) and CIDR
( Classless Inter-Domain Routing ) has been used to extend
the shortage of addresses, the huge demand of internet today
is leading to require more and more addresses thus requiring
a more reliable protocol like IPv6 which gets lots of addresses
of range 3.4x10^38.
IPv6 potentially offers enhancements, which include increased
addressing capacity and capabilities, QoS control, mobility,
built in IPSEC security and improved routing efficiency.
3. IPv6 Addressing Basics
IPv6 has a vast address space than IPv4. IPv6 address is
128 bits in length represented in Hexadecimal whereas IPv4 uses
only 32 bits.
IPv6 address consists of 8 groups of four hexadecimal digits
separated by colons and which mainly consists of 3 segments
called Global Prefix which is of 48 bits, subnet part with 16
bits and Interface ID called as Host part with 64 bits.
Example of an IPv6 address : 2001:0db8:85a3:08d3:1319:8a2e:0370:7334
The first 3 octets constitute Global Prefix, the fourth octet
constitute subnet part and the last four form the Interface
Also when web browser is used to make a https connection
to an IPv6 device, the address to be enclosed in square brackets
https://[2001:0db8:85a3:08d3:1319:8a2e:0370:7334] / home.html
Also one set of 0’s in the address can be replaced
by :: but only once this can be done as per the rule.
Ex: 2001:0db8:85a3:0000:0000:8a2e:0370:7334 is a valid
IPv6 address. To shorten the writing and presentation of addresses,
simplifications to the notations are permitted. i.e, any leading
zeroes in a group may be omitted.
Therefore the example becomes,
One or any number of consecutive groups of 0 value may be
replaced with two colons (::):
4. Embedding MAC address in
The IPv6 Modified EUI-64 Format
The actual mapping from data link layer addresses to IP interface
identifiers depends on the particular technology and it is essential
that all devices on the same network use the same mapping technique.
By far the most common type of layer 2 addresses in networking
are IEEE 802 MAC addresses, used by Ethernet and other IEEE
802 Project networking technologies. These addresses have 48
bits, arranged into two blocks of 24. The upper 24 bits are
arranged into a block called the organizationally unique identifier
(OUI), with different values assigned to individual organizations;
the lower 24 bits are then used for an identifier for each specific
The IEEE has also defined a format called the 64-bit extended
unique identifier, abbreviated EUI-64. It is similar to the
48-bit MAC format, except that while the OUI remains at 24 bits,
the device identifier becomes 40 bits instead of 24.
A form of this format, called modified EUI-64, has been adopted
for IPv6 interface identifiers. To get the modified EUI-64 interface
ID for a device, simply take the EUI-64 address and change the
7th bit from the left (the “universal/local” or “U/L”
bit) from a zero to a one.
Important Point to Note :The last 64 bits of
IPv6 unicast addresses are used for interface identifiers, which
are created in a special format called modified EUI-64. A simple
process can be used to determine the interface identifier from
the 48-bit MAC address of a device like an Ethernet network
interface card. This can then be combined with a network prefix
(routing prefix and subnet ID) to determine a corresponding
IPv6 address for the device.