Domain Network Services (DNS)

How DNS certificate works?

What is DNS?
  • DNS stands for Domain Name System.
  • It is a hierarchical distributed naming system for computers and services or any resource connected to the Internet or a private network.
  • DNS uses UDP as the transport protocol.
  • It is the client-server application. A host which wants to map a name to address or vice versa, calls a DNS client named as resolver.
  • It uses alias names for identifying the sender and receiver instead of an IP address. So the alias address has to be mapped to the IP address.
Importance of DNS
  • The DNS distributes the responsibility of assigning domain name and mapping those names to IP addresses by designating authoritative name servers for each domain.
  • Authoritative name servers are assigned to be responsible for their supported domains and may delegate authority over sub-domains to other name servers.
  • This mechanism provides distributed and fault tolerant service and was designed to avoid the need for a single central database.
  • DNS identifies the sender and receiver so they should be known to each other.
Working flow of DNS
  • When the name < -- >address mapping is necessary a host calls a resolver.
  • The resolver then accesses the closest DNS server with a mapping request.
  • If this server has the requested information, it satisfies the resolver but if it does not have the requested information, then it refers the resolver to ask other servers to provide the information.
  • The resolver receives the mapping and then checks for an error and if it finds an error then it delivers the free mapping to the requesting process.
Types of DNS Domain Names
TypesDescriptionExample
Root domainRoot domain is the top of the tree. It represents an unnamed level. Sometimes it is shown as two empty quotation marks (""), indicating a null value. When using a DNS domain name, it is stated by a trailing period (.) to indicate that the name is located at the root or the highest level of the domain hierarchyA single period (.) is used at the end of a name, such as “example.careerride.com.”
Top level domainA name used to indicate a country/region or the type of organization.'.com', which indicates a name registered to a business for commercial use on the Internet.
Second level domainVariable-length names are registered to an individual or an organization on the Internet. These names are based upon an appropriate top-level domain. It depends on the type of organization or geographic location where a name is used.'careerride.com.', which is the second-level domain name registered to CareerRide Info Pvt. Ltd. by the Internet DNS domain name registrar.
SubdomainAdditional names that an organization can create that are derived from the registered second-level domain name. These include names added to grow the DNS tree of names in an organization and divide it into departments or geographic locations.'example.careerride.com.', which is a fictitious subdomain assigned by CareerRide Info Pvt. Ltd. for use in documentation example names.

Some DNS Top-level Domain Names (TLDs)

DNS Domain NameType of Organization
comCommercial organizations
eduEducational institutions
orgNon-profit organizations
netNetworks (the backbone of the Internet)
govNon-military government organizations
milMilitary government organizations
arpaReverse DNS
“xx”Two-letter country code (i.e. us, au, ca, fr)

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