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DNS Tree

Updated Jan 19, 2018 ·

Centralized Systems​

A single database for all domain names would create major challenges.

  • Administrative Overhead
  • Poor Scalability
  • Uniqueness Issues

These limitations led DNS to adopt a distributed system, allowing better management and global uniqueness.

Hierarchical​

DNS organizes names like a tree, with multiple levels representing different domains and subdomains.

  • Distributed collection of databases forms a tree
  • Each domain name is a path in this tree
  • Organizations manage their own domains
  • Subdomains can be delegated to others

Domains can also can be divided and delegated to improve management.

  • Each domain can be split into subdomains
  • Delegated organizations can modify data freely
  • This allows scalability and easier administration

Delegation makes DNS flexible, scalable, and ensures uniqueness across the global namespace.

DNS Tree Structure​

The DNS system has multiple levels of servers that maintain the hierarchy.

  • Root Name Servers

    • At the top of the tree
    • Direct queries to appropriate top-level domain servers

  • Top-Level Domain Servers

    • Handle domains like .com, .org, .net
    • Forward requests to authoritative servers

  • Authoritative Name Servers

    • Hold the actual data for specific domains

Root Servers​

Root servers is the first point of contact of any DNS reqeust. They handle the initial queries and guide them to the correct top-level domain server.

  • Sit at the top of the DNS hierarchy
  • Receive the first DNS request from a user
  • Refer the query to the correct top-level domain server

When a user looks up a domain name, the root server sends the query to the TLD server based on the domain extension. For example, a query for example.com is directed to a .com TLD server.

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There are 13 root servers named from A to M, but each has many copies worldwide to handle traffic.

Details about each server are available at root-servers.org

Top-Level Domain Name Servers (TLD)​

TLD name servers get referrals from root servers and help move DNS queries closer to the site’s server.

  • Provide the next level of authority
  • Forward referrals to the authoritative server
  • Only know what is needed to guide the query
  • Keep each query moving toward resolution

There are several types of top-level domains that indicate the type or location of an organization.

  • Generic TLDs (gTLDs)

    • Show the type of organization or industry
    • Examples: .com, .edu, .gov, .org, .info

  • Country Code TLDs (ccTLDs)

    • Represent specific countries
    • Examples: .gr for Greece, .jp for Japan, .pl for Poland

  • Organizational Subdomains in ccTLDs

    • Countries can create subdomains for companies
    • Examples: co.uk for UK companies, com.au for Australian companies

Authoritative Name Servers​

Authoritative name servers provide the final answer in the DNS process. They hold the IP addresses for specific domains and complete the query.

  • Hold the DNS records for a domain
  • Provide the IP address for requested sites
  • Complete the resolution without further referrals

After referrals from root and TLD servers, the authoritative server gives the final response, allowing users to reach the website.

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Authority in DNS means control over a domain and responsibility to answer queries about it.