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IPv6 (Internet Protocol Version 6)


Contents

1. Introduction

Internet Protocol Version 6 (IPv6) is the next generation protocol for Internet Networking defined by IETF (Internet Engineering Task Force) which is often treated as successor to Internet Protocol Version 4 (IPv4).

2. Need for IPv6

Although IPv4 has fulfilled the requirements of internet, increasing demand and growth of internet is making it shortage of addresses which are needed by all new machines added to the internet thus arising a need for Internet Address allocation scheme that could provide addresses without getting exhausted.

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 ID.

Also when web browser is used to make a HTTP connection to an IPv6 device, the address to be enclosed in square brackets as shown

http://[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,

2001:db8:85a3:0:0:8a2e:370:7334

One or any number of consecutive groups of 0 value may be replaced with two colons (::):

2001:db8:85a3::8a2e:370:7334

4. Embedding MAC address in IPv6

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 device.

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.

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