9.1 INTRODUCTION

Domain name system (DNS) is a distributed database that offers mapping service from domain name into IP address. ^[1], ^[2] DNS helps users contact web sites or resources in Internet with simple domain names, instead of long numeric IP addresses. Since operating systems can not understand domain names, DNS translates them into IP addresses which are logical addresses of devices. DNS also offers other services such as the reverse mapping from IP addresses to domain names. ^[3]

Whenever a client application needs to communicate with another party, but it does not have any knowledge about logical addresses except domain names, it queries one of the nearest name servers and gets appropriate answers in response to that query.

DNS has been developed as a systematical delegation model and distributed domain database with hierarchy. Hierarchical name space supports flexible structure with additional extensions. Distributed database architecture augments management efficiency.

The identifier of IP version 4 and version 6 is 32-bit long and 128-bit long, respectively. Current DNS service can not be applied to IPv6 addresses because the length of IPv6 address is four times longer than that of present IPv4 address. Extensions or modifications to incorporate with IPv6 addresses are required to current DNS systems.

New record type, AAAA is defined to support 128-bit IPv6 address in DNS. ^[4] The AAAA record is just an extension of present A record type. Thus, most DNS entities will handle the new record type without much trouble.

As DNS plays...