There are several types of DNS servers, each serving a specific role in the Domain Name System. Here are the main types:
- Recursive DNS Servers: Also known as resolver servers, recursive DNS servers are responsible for resolving DNS queries on behalf of clients. When a client sends a DNS query, a recursive DNS server retrieves the requested information by querying authoritative DNS servers. Recursive DNS servers cache the responses to improve performance and reduce the load on authoritative servers.
- Authoritative DNS Servers: Authoritative DNS servers hold the actual DNS records for a specific domain. They are the final source of information for a given domain name. When a recursive DNS server receives a query for a domain, it contacts the authoritative DNS servers responsible for that domain to obtain the requested information.
- Primary (Master) Authoritative DNS Server: The primary authoritative DNS server stores the original copies of DNS records for a domain. It is the server where modifications to DNS records are made.
- Secondary (Slave) Authoritative DNS Server: Secondary authoritative DNS servers obtain copies of DNS records from the primary server and provide redundancy. They can respond to DNS queries independently if the primary server becomes unavailable.
- Caching-only DNS Servers: Caching-only DNS servers, as the name suggests, focus solely on caching DNS responses. They don’t hold authoritative information for any domain but store recently resolved DNS records in their cache. Caching-only servers help improve DNS lookup speeds by serving frequently accessed records directly from the cache without querying authoritative servers.
- Forwarding DNS Servers: Forwarding DNS servers do not resolve DNS queries themselves but instead forward the queries to other DNS servers for resolution. They are typically configured to forward queries to specific DNS servers, such as the DNS servers of an internet service provider (ISP) or public DNS resolvers like Google DNS or OpenDNS.
- Root DNS Servers: Root DNS servers form the backbone of the DNS hierarchy. They are responsible for providing information about the top-level domains (TLDs) such as .com, .org, .net, etc. There are 13 sets of root DNS servers distributed worldwide, and they are queried when resolving domain names that are not already cached.
- TLD DNS Servers: TLD DNS servers handle the DNS resolution for the respective top-level domains. For example, the .com TLD DNS servers handle queries for domain names ending with .com. TLD DNS servers store information about the authoritative DNS servers for individual domains within their TLD.
These different types of DNS servers work together to ensure the efficient and accurate resolution of domain names to their corresponding IP addresses. By distributing responsibilities across various server types, the DNS system can handle the massive scale of internet domain name resolution effectively.