User's Manual

74-1
Chapter 74 DNSv4/v6 Configuration
74.1 Introduction to DNS
DNS (Domain Name System) is a distributed database used by TCP/IP applications to translate domain
names into corresponding IPv4/IPv6 addresses. With DNS, you can use easy-to-remember and signification
domain names in some applications and let the DNS server translate them into correct IPv4/IPv6 addresses.
There are two types of DNS services, static and dynamic, which supplement each other in application. Each
time the DNS server receives a name query it checks its static DNS database first before looking up the
dynamic DNS database. Some frequently used addresses can be put in the static DNS database, the
reduction the searching time in the dynamic DNS database would increase efficiency. The static domain name
resolution means setting up mappings between domain names and IPv4/IPv6 addresses. IPv4/IPv6
addresses of the corresponding domain names can be found in the static DNS database when you use some
applications. Dynamic domain name resolution is implemented by querying the DNS server. A user program
sends a name query to the resolver in the DNS client when users want to use some applications with domain
name, the DNS resolver looks up the local domain name cache for a match. If a match is found, it sends the
corresponding IPv4/IPv6 address back to the switch. If no match is found, it sends a query to a higher DNS
server. This process continues until a result, whether success or failure, is returned.
The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource
participating in the Internet. It associates various information with domain names assigned to such
participants. Most importantly, it translates humanly meaningful domain names to the numerical (binary)
identifiers associated with networking equipment for the purpose of locating and addressing these devices
world-wide. An often used analogy to explain the Domain Name System is that it serves as the "phone book"
for the Internet by translating human-friendly computer hostnames into IP addresses.
The Domain Name System makes it possible to assign domain names to groups of Internet users in a
meaningful way, independent of each user's physical location. Because of this, World-Wide Web (WWW)
hyperlinks and Internet contact information can remain consistent and constant even if the current Internet
routing arrangements change or the participant uses a mobile device. Internet domain names are easier to
remember than IP addresses such as 208.77.188.166(IPv4) or 2001:db8:1f70::999:de8:7648:6e8 (IPv6).
People take advantage of this when they recite meaningful URLs and e-mail addresses without having to
know how the machine will actually locate them.
The Domain Name System distributes the responsibility for assigning domain names and mapping them to
Internet Protocol (IP) networks by designating authoritative name servers for each domain to keep track of
their own changes, avoiding the need for a central register to be continually consulted and updated.
In general, the Domain Name System also stores other types of information, such as the list of mail servers
that accept email for a given Internet domain. By providing a world-wide, distributed keyword-based
redirection service, the Domain Name System is an essential component of the functionality of the Internet.