Domain system

• Domain Name System (DNS)


  A decentralized naming system that is used to translate domain names (such as www.example.com) into IP addresses (such as 192.0.2.1) that can be used by computers to communicate over the Internet
• DNS system


  • Consists of a network of servers that are organized into a hierarchical structure
  • At the top of the hierarchy are the root servers, which contain information about the top-level domains (such as .com, .org, .net, etc.)
  • Below the root servers are the authoritative name servers for each domain, which contain information about the specific domain names and IP addresses
• Domain name resolution process


  1. User types a domain name into their web browser

  2. Browser sends a query to a DNS resolver (typically provided by their Internet Service Provider)

  3. Resolver looks up the appropriate authoritative name server for the domain and requests the IP address for the domain name

  4. Authoritative name server responds with the IP address

  5. Resolver returns the IP address to the user's web browser

  6. Browser can then establish a connection with the appropriate server to retrieve the web page or other content
• Uniform Resource Locator (URL)


  A web address which uniquely identifies a document over the internet
• Types of URL


  • Absolute URL
  • Relative URL
• Absolute URL


  A complete address of a resource on the web, comprising protocol, server name, path name and file name
• Relative URL


  A partial address of a webpage, omitting the protocol and server part
• Absolute URL vs Relative URL


  Absolute URL is used to link web pages on different websites, while Relative URL is used to link web pages within the same website
• Domain Name Space


  • Hierarchy in the internet naming structure, with a root at the top
  • Domain name space can be partitioned into sub domains and further partitioned
• Name Server


  • Contains the DNS database, comprising various names and their corresponding IP addresses
  • Information is distributed among many DNS servers
  • Hierarchy of servers is same as hierarchy of names
  • The entire name space is divided into zones
• Types of Name Servers


  • Root Server
  • Primary Server
  • Secondary Server
• Root Server


  Top level server which consists of the entire DNS tree, but does not contain the information about domains and delegates the authority to the other servers
• Primary Server


  Stores a file about its zone, has authority to create, maintain, and update the zone file
• Secondary Server


  Transfers complete information about a zone from another server, does not have authority to create or update a zone file
• DNS Working


  1. User types domain name into browser

  2. Browser asks local DNS server for IP address

  3. Local DNS server forwards request to root DNS server

  4. Root DNS server provides delegation to top-level domain server

  5. Local DNS server asks top-level domain server for IP address

  6. Top-level domain server provides IP address of domain server

  7. Local DNS server sends IP address to user's browser
• The DNS is the distributed database that maps domain names to IP addresses.
• DNS servers are responsible for resolving domain name requests from clients.
• DNS servers are used to translate human-readable hostnames into machine-readable IP addresses, allowing computers on different networks to communicate with one another.
• The DNS is used to translate domain names into IP addresses.
• A DNS server can be configured as an authoritative or non-authoritative server.
• A DNS server can be configured as an authoritative name server or a caching name server.
• A DNS server can be configured as an authoritative or non-authoritative server.
• A DNS query starts at the client computer (e.g., web browser) and travels through several levels of DNS servers until it reaches the authoritative DNS server for the requested domain.
• There are different types of DNS servers including authoritative servers (primary and secondary), recursive servers, caching servers, and forwarding servers.
• A DNS query involves multiple steps including sending a request to a local DNS server, which then contacts other DNS servers until an answer is found.
• An authoritative DNS server has information about specific domains and their corresponding IP addresses.
• An authoritative name server has information about all domains it manages directly.
• DNS servers use UDP packets with port number 53 to communicate with each other.