Of what the service of DNS consists?

Domain Name System

The Domain Name System (DNS) is and hierarchic a distributed database that stores information associated to names of domain in networks as Internet. Although as data base the DNS is able to associate different types from information from each name, the most common uses are the allocation of names of domain to directions IP and the location of the servers of e-mail of each domain.

The allocation of names to directions IP is certainly the most well-known function of protocols DNS. For example, if direction IP of site FTP of reliable-hosts.com is 200.89.183.194, most people arrive at this equipment specifying ftp.reliable-hosts.com and not it direction IP. In addition to being easier to remember, the name is more trustworthy. The numerical direction could change for many reasons, without it must change the name.

Initially, the DNS was born from the necessity to easily remember the names of all the connected servers to Internet. At the beginning, SRI (now SRI International) lodged a called file HOSTS that contained all the well-known names of domain (technically, this file still exists - the majority of the present operating systems still can be formed to review their file hosts). The explosive growth of the network caused that the system of names centralized in file HOSTS would not be practical and in 1983, Paul Mockapetris published RFCs 882 and 883 defining what nowadays the modern DNS has evolved. (These RFCs have been obsolete by the publication in 1987 of RFCs 1034 and 1035).

Components

For the practical operation of system DNS three main components are used:

* Clients DNS: A program client DNS who executes himself in the computer of the user and who generates requests DNS of resolution of names to a servant DNS (For example: What direction IP corresponds to nombre.dominio);
* Servers DNS: That they answer requests of the clients. The recursivos servers have the capacity to resend the request to another servant if they do not have the asked for direction;
* and the Zones of authority, portions of the space of domain names that store the data. Each zone of authority includes a domain at least and possibly its subdomains, if these last ones are not delegated to other zones of authority.

Understanding the parts of a domain name.

A domain name usually consists of two or more parts (technically labels), separated by points when it is written them in the form of text. For example, www.mahomedalid.org or es.Wikipedia.org

* To the label located to the right top-level domain is called to him more (English < Top Level Domain). As org in www.mahomedalid.org or es.Wikipedia.org
* Each label to the specific left a subdivision or subdomain. Absolute nondependency notices that “subdomain” expresses relative dependency. In theory, this subdivision can have up to 127 levels, and each label to contain up to 63 characters, but restricted to that the length overall of the name of the domain does not exceed the 255 characters, although actually the domains are almost always much more short.
* Finally, the part more to the left of the domain usually expresses the name of the machine (in English hostname). The rest of the simply specific name of domain the way to create a logical route to the required information. For example, the es.Wikipedia.org domain would have the name of the machine “is”, although in this case it does not talk about in particular to a physical machine.

The DNS consists of a hierarchic set of servers DNS. Each domain or subdomain has one or more zones of authority than publish the information about the domain and the names of services of any domain including. The hierarchy of the zones of authority agrees with the hierarchy of the domains. At the beginning of that hierarchy one is the servers root: the servers who respond when he looks for to solve a domain of first and second level…

Types of servers DNS

Bind • PowerDNS • MaraDNS • djbdns • pdnsd • MyDNS • DNS (Windows 2000/2003)

Types of resolution of domain names

Two types of consultations exist that a client can make a servant DNS:

* Iterative
* Recursiva

In the recursivas consultations the servant repeats the same basic process (to consult a remote servant and to follow any reference) until he obtains the answer to the question.

The iterative consultations, or iterative resolution, consists of the best answer than the servant of names can give. The servant of names consults his local data (including its cache) looking for the asked for data.

When it exists more of an authoritarian servant for a zone, BIND uses the smaller value in the metric RTT (Round-Trip Time) to select the servant. The RTT is a measurement to determine how much a servant in responding a consultation takes.

The process of normal resolution occurs of the following way:

1. The servant To receives a recursiva consultation from client DNS.
2. The servant To sends an iterative consultation to B.
3. Servant B refers to A another servant of names, including a C.
4. The servant To sends an iterative consultation to C.
5. Servant C refers to A another servant of names, including a D.
6. The servant To sends an iterative consultation to D.
7. Servant D responds.
8. The servant To returns the answer when solving.
9. Solving delivery lta to the program that asked for the information.

Types of registries DNS

* A = Address – (Direction) This registry is used to translate names of hosts to directions IP.
* CNAME = Canonical Yam – (Canónico Name) it is used to create additional names of hosts, or alias, for hosts of a domain. It is used when they are estan running multiple services (as FTP and web server) in a servant with a single direction IP. Each service has its own entrance of DNS (as ftp.ejemplo.com. and www.ejemplo.com.). this also is used when you run multiple servers HTTP, with different names, on the same host.
* NS = Server Yam – (Servant of Names) It defines the association that exists between a domain name and the servers of names that stores the information of this domain. Each domain can be associated to an amount anyone of servers of names.
* MX (registry) = Exchange Mail – (Registry of Interchange of Mail) It associates a name of domain to a list of servers of interchange of mail for that domain.
* PTR = Pointer – (Indicating) Also known as ‘inverse registry’, it works to the inverse one of the registry To, translating IPs in domain names.
* SOA = Start of authority – (Authority of the zone) It provides information on the zone.
* HINFO = Host INFOrmation – (Information of the computer science system) Description of host, allows that people meet the type machine and operating system to whom corresponds a domain.
* TXT = TeXT - (textual Information) It allows the domains to identify itself of arbitrary ways.
* LOC = Location - It allows to indicate the coordinates of the domain.
* WKS - Generalization of registry MX to indicate the services that the domain offers. Obsolete for SRV.
* SRV = Services - It allows to indicate the services that the domain offers. RFC 2782
* SPF = Sender Policy Framework - Aid to fight the Spam. In this record specific what or as hosts is authorized to send mail from the given domain. The servant who receives consultation the SPF to compare the IP from which arrives to him, with the data of this registry.

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