Domain name server

Parent element: Name server

This way of managing names is to assign different groups to the names of the subsystems. Each layer in the system is called a domain, and each domain is separated by a point.
The so-called domain name server (namely, Domain Name Server, called Name Server, DNS) is actually the host with the domain name system. It is a hierarchical database that performs name resolution.

DNS can allow a name server to "delegate" a part of its name service (a known zone) to a secondary server to implement a hierarchical namespace. In addition, the DNS provides additional information, such as system aliases, contact information, and the host that acts as a mail center for a group or system domain.

Currently, the limit for the length of each domain name is 63 characters, and the total length of the domain name can not exceed 253 characters. Domain names are also limited to a subset of ASCII characters, which means that many other languages ​​can not correctly represent their names and words. Based on the IDNA system based on the Punycode code, Unicode strings can be assigned to a valid DNS character set, which some records have validated and adopted as an alternative solution.

In addition, there is no distinction between upper and lower case in the domain name. The domain name generally can not exceed level 5, the domain level from left to right becomes higher and the top-level domain contains a lower-level domain.

The domain name is unique on the Internet.
When the advanced subdomains are the same, low-level subdomains are not allowed to duplicate. A server can only have one IP address, but it can have several domain names.

The domain name is the "second generation" of network addressing. The URL is an abbreviation of Uniform Resource Location, translated as "Uniform Resource Locator".
The DNS system is managed by a wide variety of DNS software, including:
BIND (Berkeley Internet Name Domain), which is the most widely used DNS software.
DJBDNS (DNS implementation of Dan J Bernstein)
MaraDNS
NSD (name of the daemon server)
PowerDNS

Any computer network that uses IP can use DNS to implement its own private name system. However, the term "domain name" is the most used when referring to domain names implemented in Internet public DNS systems.
This is based on 13 global "root servers", with the maintenance organization in addition to three of them, all located in the United States. Starting with the 13 root servers, the remaining Internet DNS namespaces are delegated to other DNS servers that provide specific portions of the DNS namespace.

The "owner" of a domain name can be found by consulting the whois database; for most gTLDs, ICANN maintains the basic WHOIS, and the domain registrar that controls that domain maintains the WHOIS details. For domain registrations with more than 240 national domain names (ccTLD), the respective country maintains its WHOIS.

The current methods of DNS system control are often blamed. The most frequently targeted focus is the abuse of DNS by monopolistic or quasi-monopolistic companies, such as VeriSign, and the distribution of top-level domains.

Others claim that many DNS server software does not work well for dynamic IP allocation, although this is a bug of some specific implementations instead of the protocol itself.
DNS uses TCP and UDP port 53.