What Are the 3 Classes of DNS Server?


Angela Bailey

When it comes to understanding the Domain Name System (DNS), it’s essential to be familiar with the three different classes of DNS servers. These classes, which include caching resolvers, authoritative servers, and root servers, play a crucial role in the functioning of the DNS system. In this article, we will delve into each class and explore their significance in detail.

Caching Resolvers

The first class of DNS servers is caching resolvers. These servers act as an intermediary between clients and the DNS infrastructure.

When a client requests a domain name resolution, the caching resolver checks its cache to see if it has a record of that domain name’s IP address. If it does, it can provide an immediate response without having to query other DNS servers.

Key Features:

  • Caches Responses: Caching resolvers store recently resolved domain names’ IP addresses to improve response times for subsequent requests.
  • TTL (Time-to-Live): Caching resolvers honor the TTL value provided by authoritative servers. Once the TTL expires, they discard the cached record and perform a fresh lookup.
  • Recursive Queries: They handle recursive queries by contacting multiple DNS servers until they obtain a final response for the client.

Authoritative Servers

The second class of DNS servers is authoritative servers. These servers are responsible for storing and providing authoritative information about specific domains. When a caching resolver receives a query for which it doesn’t have a cached record, it contacts an authoritative server to obtain the necessary information.

Key Features:

  • Serves Authoritative Information: Authoritative servers hold the official records for specific domains, including the IP addresses associated with them.
  • Responds to Queries: They respond to queries received from caching resolvers by providing the requested DNS information.
  • Name Server Records: Authoritative servers also provide information about which name servers are authoritative for a particular domain.

Root Servers

The third class of DNS servers is root servers. These servers form the foundation of the DNS hierarchy.

There are 13 sets of root servers distributed worldwide. Each set consists of multiple physical servers managed by different organizations. The primary function of root servers is to provide referrals to authoritative servers based on top-level domains (TLDs) like .com, .org, etc.

Key Features:

  • Distribute Referrals: Root servers distribute referrals to caching resolvers, guiding them towards the appropriate TLD authoritative server based on the requested domain name.
  • Manage Root Zone File: They manage the root zone file, which contains a list of TLDs and their corresponding authoritative servers.
  • Anycast Technology: Many root server operators use anycast technology to provide a distributed network infrastructure for improved resilience and performance.

In Conclusion

In summary, understanding the three classes of DNS servers is crucial for comprehending how domain name resolution works. Caching resolvers expedite subsequent requests by storing resolved domain names in their cache.

Authoritative servers hold official records for specific domains and respond to queries from caching resolvers. Root servers form the backbone of the DNS hierarchy and distribute referrals based on top-level domains. By familiarizing ourselves with these classes, we gain a deeper understanding of the DNS system’s inner workings.

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