Difference Between Interactive Query abd Recursive Query ?

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In the context of DNS (Domain Name System), interactive and recursive queries are two different types of DNS queries used by DNS resolvers to resolve domain names into IP addresses. They serve distinct purposes and involve different levels of interaction between the resolver and DNS servers. Here's an explanation of each type with examples:

1. Interactive Query:

  • Interactive queries are DNS queries in which the DNS resolver requests information from a DNS server but expects that server to provide a full and complete answer. If the queried DNS server does not have the requested information, it can either provide a referral to another authoritative DNS server or return a negative response.

  • In an interactive query, the DNS resolver communicates directly with authoritative DNS servers and can involve multiple iterations until the resolver receives a complete answer or determines that the requested domain does not exist.

Example of an Interactive Query:

Suppose a user wants to access the website "www.example.com." The DNS resolver initiates an interactive query by sending a query to a DNS server. The resolver expects a complete answer, including the IP address of the "www.example.com" website.

  1. Resolver queries the root DNS server for "www.example.com."
  2. The root DNS server responds with a referral to the authoritative DNS server for the ".com" top-level domain.
  3. Resolver queries the ".com" authoritative DNS server.
  4. The ".com" authoritative DNS server responds with a referral to the authoritative DNS server for "example.com."
  5. Resolver queries the "example.com" authoritative DNS server.
  6. The "example.com" authoritative DNS server responds with the IP address of "www.example.com."
  7. The resolver caches the response and returns the IP address to the user.

2. Recursive Query:

  • Recursive queries are DNS queries in which the DNS resolver requests information from a DNS server and expects that server to perform all necessary steps to provide a complete answer. The DNS server may have to query other DNS servers on behalf of the resolver to fulfill the request.

  • Recursive queries are often used by DNS resolvers provided by internet service providers (ISPs) or public DNS services (e.g., Google DNS, OpenDNS). These resolvers handle the entire resolution process, including contacting authoritative DNS servers.

Example of a Recursive Query:

Using the same example of accessing "www.example.com":

  1. The DNS resolver sends a recursive query to its configured DNS server (e.g., ISP's DNS server or a public DNS service).
  2. The DNS server at the resolver's end queries the root DNS server on behalf of the resolver, requesting information for "www.example.com."
  3. The root DNS server responds with a referral to the ".com" authoritative DNS server.
  4. The DNS server continues the query process by contacting the ".com" authoritative DNS server.
  5. The ".com" authoritative DNS server responds with a referral to the "example.com" authoritative DNS server.
  6. The DNS server queries the "example.com" authoritative DNS server.
  7. The "example.com" authoritative DNS server responds with the IP address of "www.example.com."
  8. The DNS server caches the response and sends the IP address to the resolver.
  9. The resolver caches the response and returns the IP address to the user.

In summary, the key difference between interactive and recursive queries is the level of involvement and responsibility of the DNS resolver.

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