DNS (Domain Name System, Indonesian: Domain Naming System) is a system that stores information about hostnames and domain names in the form of distributed databases (Distributed databases) in a computer network, for example: the Internet. DNS provides the IP address for each host name and log every mail transmission server (mail exchange server) that receives electronic mail (email) for each domain.
DNS provides an important service to the Internet, where computer and network hardware work with IP addresses to perform tasks such as addressing and routing (routing), humans in general prefer to use the host name and domain name, example is the appointment of a universal source (URL) and e-mail address. DNS connects this need.
A brief history of DNS
The use of the name as pengabstraksi machine address in a computer network that is better known by humans to defeat the TCP / IP, and back to the days of ARPAnet. In the past, every computer on the network computer using the file HOSTS.TXT from SRI (now SIR International), which maps an address to a name (technically, these files still exist - most modern operating systems use either raw or through configuration, can view the Hosts file to match a host name into an IP address before performing a search via DNS). However, that system had inherent limitations because of the obvious requirement that every time a computer's address changed, any system that wanted to communicate with the computer would need an update to its Hosts file.
With the development of computer networks, requires a system that could be developed: a system that can change the host address only in one place, other hosts will learn the dynamic perubaha. This is the control.
[edit]The Core Players
Management of the DNS system consists of three components:
- DNS resolver, a client program that runs on a user's computer, which makes DNS request from an application program.
- recursive DNS server, which searches through the DNS in response to requests from the resolver, and return the answer to the resolveris;
and ...
- authoritative DNS servers that provide answers to requests from recursor, either in the form of an answer, or in the form of delegation (eg: refer to the authoritative DNS servers , etc.)
[edit]Understanding the parts of a domain name
- The rightmost label conveys the top-level domains - domain level top / high (eg, the address www.wikipedia.org has a top-level domain org).
- Each label to the left specifies a subdivision or subdomain of the domain is higher. Note that "subdomain" expresses relative dependence, not absolute. Example: wikipedia.org comprises a subdomain of the domain org, and id.wikipedia.org may form a subdomain of the domain wikipedia.org (in practice, id.wikipedia.org actually represents a host name - see below). In theory, this subdivision can reach a depth of 127 levels, and each label can contain up to 63 characters, for a total length of a domain name does not exceed 255 characters. But in practice, some domain name registrants (domain name registry) has fewer limits.
- Finally, the far left of the domain name (usually) state the name of the host. The rest of the domain name specifies a way to build a logical path to the information needed; hostname is the actual target system name for which its IP address. Example: domain namewww.wikipedia.org has the hostname "www".
DNS has a hierarchical set of DNS servers. Each domain or subdomain has one or more authoritative DNS Servers (authoritative DNS servers) that publish information about the domain and server names of any domains "beneath" her. At the top of the hierarchy, there are root servers- the parent name server: server in question when looking for (complete/resolving) of a domain name of the highest (top-level domain).
[edit]An example of the theory of recursive DNS
An example may clarify this process. Suppose there is an application that requires finding the IP address of www.wikipedia.org. The application asks the DNS recursor local.
- Before starting, recursor need to know where to find the root servers; administrators of recursive DNS servers manually set (and periodically update) a file called the root hints zone (manual root DNS) which states alamt IP-address of the server.
- The process begins by recursor who is asking the root servers - for example, a server with IP address "198.41.0.4" - the question "whether the IP address of www.wikipedia.org? "
- Root server replies with a delegation, meaning roughly: "I do not know the IP address of www.wikipedia.org, but I do know that the DNS server at 204.74.112.1 has information about the domain org. "
- Recursor local DNS then asks that DNS server (ie: 204.74.112.1) the same questions given to the root servers. "What the IP address ofwww.wikipedia.org? ". (Generally) will get a similar reply, "I do not know the address of www.wikipedia.org, but I do know that the server 207 142 131 234 has information of the domain wikipedia.org. "
- Finally, the question is transferred to the third DNS server (207 142 131 234), who responded with the required IP address.
[edit]Understanding domain registration and glue records
Reading the example above, you may ask: "how does the DNS server 204.74.112.1 know which IP address given for the domainwikipedia.org? " At the beginning of the process, we noted that a DNS recursor have an IP address of the root servers are (more or less) recorded explicitly (hard coded). Similar to this, the server name (name servers) that are authoritative for top-level domains that rarely changes.
However, the name servers that provide authoritative answers for generic domain names may change relatively frequently. As part of the process of registering a domain name (and some time thereafter), registrars provide registration with the server name that will be authoritative for that domain name, so when registering wikipedia.org, the domain with the name servers gunther.bomis.com andzwinger.wikipedia . org in the registries. org. Then, from the example above, when the server 204.74.112.1 identified as receiving a request, the DNS server scans the list of existing domain, looking for wikipedia.org, and returns the name servers that connect to the domain.
Typically, the server name appear in order of name, other than by IP address. This has led to a string other than request the DNS to resolve the name of the server name, when an IP address of the server name to get a registration in the parent zone, the computer network programmer called a glue record (list attached?)
[edit]DNS in practice
When an application (eg web broswer), wants to find the IP address of a domain name, the application does not necessarily follow all the steps outlined in the theory above. We will first look at the concept of caching, then the operation of DNS in "real world".
[edit]Caching and time to live (caching and time to live)
Due to the large number of requests from systems such as DNS, DNS designer wanted the provision of a mechanism that can reduce the load of each server control. The mechanism devised provided that when a DNS resolver (client) receives a DNS response, it will be in the cache for a specified period. A value (which is set by the administrator of the DNS servers that provide answers) called it a time to live (life), or TTL defines that period. Once a response goes into cache, the resolver will consult its answer is stored in the cache is, only when the TTL after (or while emptying the answer from memory administrator resolver manually) then the resolver contacts the server DNS to the same information.
[edit]Time propagation (propagation time)
One important result of the spread of architecture and the cache is changes to the DNS does not always immediately effective in large scale / global. The following example will probably explain it: If an administrator has set a TTL of 6 hours for the host www.wikipedia.org, and then change the IP address of www.wikipedia.org at 12:01 pm, the administrator must consider that there are (at least) one individual which stores the cached response with the old value at 12:00 pm will not consult the DNS server to pk 18:00. The period between 12:00 pm and 18:00 pk in this example is called the propagation time (propagation time), which can be defined as a period of time that begins when there are changes to a DNS record and ends after the maximum time specified by the TTL passed . This will lead to logical considerations are important when making changes to DNS: not all will see the same thing as you can see. can help explain this.
[edit]DNS in the real world
In the real world, users do not deal directly with the DNS resolver - they were dealing with a program like a web brower (Mozilla Firefox,Safari, Opera, Internet Explorer, Netscape, Konqueror , etc. and mail clients (Outlook Express, Mozilla Thunderbird etc. ). When users perform a DNS lookup request activities (generally, almost all activities that use the Internet), the program sends a request to the DNS resolver in the operating system.
DNS resolver will always have a cache (see above) containing recent lookups. If the cache can provide answers to the requests of DNS, the resolver will use a value that is in the cache to the program requires. If the cache does not have an answer, the resolver will send requests to a specific DNS server. For most home users, Internet Service Provider (ISP) that connects the computer will usually supply this DNS server: such a user will server addresses manually or use DHCP to set it. If the system administrator has configured the system to use their own DNS servers, DNS resolvers will generally point to their name servers. This name server will follow the process outlined in the theory of control, whether they find the answer or not. The search results will be given to the DNS resolver; assumed to have found the answer, the resolver will save the result in the cache for future use, and provide results to the software that asks the DNS lookup.
As the final part of this complexity, some applications such as web browsers also have a DNS cache on their own, the goal is to reduce the use of reference DNS resolver, which will increase the difficulty to perform debugging DNS, which causes confusion more accurate data.Cache like this generally have a brief period in a matter of 1 minute.
[edit]Other DNS applications
The system outlined above provides a simplified scenario. DNS includes several other functions:
- Host names and IP addresses do not mean to connect on a one-to-one. Many hostnames may correspond to a single IP address: combined with virtual parenting (virtual hosting), this allows one computer to serve many web sites. In addition, a host name can represent multiple IP addresses: this will help the fault tolerance (fault tolerance and load distribution (load distribution), also allows a site to move from one physical location to physical location seamlessly.
- There are quite many uses DNS besides translating names to IP addresses. Example:, mail transfer agents Mail transfer agents (MTA)uses DNS to find the purpose of sending E-mails to certain addresses. Domain mapping informing exchange is provided via the MX record (MX record) that enhance additional layer of fault tolerance and load distribution in addition to the mapping function names to IP addresses.
- Framework for Regulation of Shipping (Sender Policy Framework) controversially takes advantage DNS record type, the TXT record.
- Provide flexibility to computer failure, multiple DNS servers provide protection for each domain. Precisely, the thirteen root servers (root servers) used by the entire world. DNS programs or operating systems have an IP address from the server. The United States has, at least nominally, all but three of the root servers. However, because many root servers actually implement anycast, which allows many different computers can share the same IP address to send one type of services through a wide geographic area, many servers that are physically (rather than nominal) is located outside the United States.
DNS uses TCP and UDP ports on your computer port 53 to serve requests. Almost all DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. TCP generally get involved only when the reply data size exceeds 512 bytes, or for such zone DNS zone transfers
[edit]Types of DNS records
Several important groups of data stored in the DNS are as follows:
- A record or address record maps a host name to IP address 32-bit (for IPv4).
- AAAA record or IPv6 address record maps a host name to IP address 128-bit (for IPv6).
- A CNAME record or canonical name record makes one domain name an alias. Domains that are my aliases have all the subdomains and DNS record as the original.
- [MX record]] ' , or mail exchange record maps a domain name to the list of mail exchange servers for that domain.
- PTR record or pointer record maps a host name to a canonical name for that host. Making the PTR record for a host name in the domain in-addr.arpa representing an IP address behind the quest to apply DNS (reverse DNS lookup) to the address. For example (as of writing this article), www.icann.net have an IP address 192.0.34.164, but a PTR record mapping,, 164.34.0.192.in-addr.arpa to name kanoniknya: referrals.icann.org.
- NS record or name server record maps a domain name to a list of DNS servers for that domain. Representation depend on NS records.
- SOA record or start of authority records (Start of Authority), the DNS server providing authoritative information about an Internet domain.
- SRV record is a record of the location in general.
- Notes TXT allows an administrator to insert arbitrary text into a DNS record, this record is used in the specification Sender Policy Framework.
Other types of records simply provide information
(for example, notes LOC gives the location of a host of physical, or experimental data (eg, record WKS provide a list of servers that provide services that are known (well-known service) such as HTTP or POP3 to a domain.
[edit]Domain names diinternasionalkan
Domain names must use only a subset of characters ASCII, this prevents some of the language to use their local names or words. ICANNhas approved the Punycode -based system of IDNA, which maps a string of Unicode to the character set of the valid DNS, as a workaround for this problem, and some registries have adopted this method of IDNs.
[edit]DNS software
Several types of DNS software implement the DNS, some of them:
- BIND (Berkeley Internet Name Domain)
- djbdns (Daniel J. Bernstein's DNS)
- MaraDNS
- QIP (Lucent Technologies)
- NSD (Name Server Daemon)
- PowerDNS
- Microsoft DNS (for the server edition of Windows 2000 and Windows 2003)
Utility-oriented control include:
- dig (the domain information Groper)
[edit]legal users of domains
[edit]The registrant (registrant)
None of the individuals in the world who "owns" a domain name unless the Network Information Centre (NIC), or the domain name registrant (domain name registry). Most of the NIC in the world receive an annual fee from a legal user in order for the legal user to use the domain name. So a kind of rental agreement occurs, depending on the terms and conditions of applicants. Depending on beberpa naming rules of the registrant, a legal user known as "registrars" (registrants) or as "domain holders" (domain holders)
ICANN holds a complete list of domain registries around the world. Anyone can find the legal user of a domain by searching through databases WHOIS held by most domain registries.
In (more or less) 240 country code top-level domains (ccTLDs), the domain registries hold the authoritative WHOIS (registrant, name servers).For instance, DENIC, NIC Indonesia, holds the authoritative WHOIS to a domain name. ID.
However, some domain registries, such as VeriSign, using the model-user registrant. For domain names. COM and. NET, domain registries, VeriSign holds a basic WHOIS) the holder of the domain and server name). Anyone can find the detailed WHOIS (Registrant, name servers, expiry dates, etc.) at the registrars.
Since about 2001, most applicants gTLD (. ORG,. BIZ,. INFO) have adopted the method penfatar "thick", keeping the authoritative WHOIS in the various registries instead of the registrars.
[edit]Administrative Contact (Administrative Contact)
The domain holder is usually appointed the administrative contact to handle domain names. Management functions delegated to administrative contacts that include (among others):
- imperative to follow the terms of the domain registrant for the purpose of having the right to use the domain name
- authorization to update the physical address, address email and phone number and so forth via WHOIS
[edit]Technical Contact (Technical Contact)
A technical contact manages the name servers of a domain name. Some of the many functions of a technical contact include:
- ensure that the configuration of the domain name to follow the terms of the domain registrant
- update domain zone
- provide 24x7 functionality to the server name (which create a domain name can be accessed)
[edit]Contact Payments (Billing Contact)
[edit]Server Name (Name Servers)
Called the authoritative name servers that the domain name zone of a domain name.
[edit]Politics
Many investigators have voiced criticism of the methods used currently to control ownership of domains. Generally, critics claim abuse by monopolies, such as VeriSign Inc. and the problems with the appointment of top-level domain (TLD). International Institute of ICANN (Internet Corporation for Assigned Names and Numbers) maintenance domain name industry.
