Domain Name System (DNS) is a distributed database TCP / IP applications for providing the host name and IP
routing information about the conversion and e-mail between the site. Distributed mentioned here refers to a single site on the I nternet is not
to have all the information. Each site (such as departments of the University, campus, the company or in the company) to retain its own
information database and run a server program for use by other systems (clients) on the I nternet query. DNS provides the
protocol allows the server and client programs communicate with each other.
From the application point of view, access to the DNS is accomplished through an address resolver (resolver). In U nix
host, mainly through the two resolver library function gethostbyname (3) and gethostbyaddr (3) access
, which are connected to the application when the application is compiled together. The former receiving host name returned an IP address, and the latter
receives an IP address to find the host name. Parser by one or more name servers to accomplish this conversion.
Figure 4 - 2 indicates the resolver is usually part of the application. The parser is not as TCP / IP protocol that is the operating
system kernel. Another basic concept of the FIG is noted: in an application program requests a TCP connection open or
before sending a UDP datagram. Heart shall convert a host name to an IP address. TCP / IP operating system kernel
protocol family did not know it for DNS.
RFC 1034 [Mockapetris 1987a] illustrates the concept and function of DNS, RFC 1035 [Mockapetris 1987b]
Detail of the specification and implementation of DNS. The most common version of the DNS (including parser and name server) is BIND -
Berkeley I nternet domain name server. The server is referred named. [D anzig, O braczka and Kumar 1992] analysis of
the traffic generated in the DNS WAN.
14.2 DNS foundation
DNS name space and U nix file system similar, with a hierarchical structure. This level of organization
Each node (FIG. 14 - is a circle) has a length of 63 characters identify up. The tree roots are no
special node identifier. All call-in does not distinguish between uppercase and lowercase. Any name of a node is to the domain tree
in series from the node up to the top domain, using a middle point "." Separated these domains (Note that this U nix file
forming system different path, the file path is sequentially downward from the root formation). Each node in the tree domain must have a
unique name, the domain name but different nodes in the tree may use the same identification.
. "" Domain names ending point is called absolute domain fully qualified domain name or the FQDN (Full Qualified! The Domain
N AME), e.g. sun. Tuc. Noao. Edu .. If a domain name does not end with a dot, it is considered that the domain name is incomplete.
How to make a complete domain relies on the use of DNS software. If an incomplete domain name consists of two or more of the composition of labels
It believes that it is complete; or join a local suffix to the right of the domain name. For example, by adding the local domain sun
suffix. Tuc. Noao. Edu. Become complete.
: Top-level domain is divided into three
special fields 1) arpa is used as an address to a name conversion (we will introduce in Section 145).
2) 7 3 characters long common domain. Some books will also be referred to these domains organizational domain.
3) All of the 2-character country code field are based on ISO 3 1 6 6 defined in these domains is called national domain, or geographic
region.