2.1 INTRODUCTION

IPv6 is a new version of Internet protocol which is expected to substitute IPv4. It is very difficult to predict exactly when IPv4 will eventually come to an end. However, most experts in internet protocol area expect that the coexistence of two protocols will be lasted for a long time. As a successor of IPv4, IPv6 will bring lots of advantage over IPv4 as follows: ^[1]

• Expanded addressing capabilities

  The size of IPv6 address is 128-bit length and four times as long as the address length of IPv4. This increased length enables various desirable features in IPv6 possible, such as hierarchical delegation and management of addressing space, virtually unlimited number of address assignment to internet devices, and autoconfiguration of internet devices. Exaggeratingly, it may be said that stars in the sky are addressable with IPv6 addressing space. Address autoconfiguration and huge addressing space are mostly emphasized points in IPv6. ^[2]

• Simplified header format The size of IPv4 Header is ranged from 20 bytes to 20 plus option field length, but the option field is highly variable to know or determine in advance from where the data field will start. Some fields in IPv4 Header are dropped or moved into Option Header to simplify and quantify to reduce the common processing cost of packets in IPv6.

• Autoconfiguration

  The autoconfiguration is the most fascinating point in adopting IPv6. IPv6 enabled device is able to configure itself dynamically when it plugs in. IPv6 interface is given with several identifiers in accordance...