Recursive Lookup ● A server does it all

The iterative technique works well, but if Alice’s computer is connected via a slow link to the Internet, the response time might be slow to make all three queries. So a second technique is built into the DNS message structure, that being a recursive lookup.

Alice’s computer has an IP address of a DNS server. This is typically a configuration option or automatically provide by a Dynamic Host Configuration Protocol or DHCP message. How this occurs is beyond our scope.

Alice’s computer sends a DNS Query message to the DNS server asking for “Bob.Example.org”.

The DNS server will then do the same process as if Alice’s computer did all the work and when completed send only one response with the final answer to Alice’s computer.

The DNS server may have faster connections to the other DNS servers so the process will be faster.

The DNS server may also be providing this service to many users and can hold on to the information or cache the data so that it does not have to repeatedly request the same information from all the servers. A clear example would be that once the TLD’s name servers are known, they don’t have to be check again for a long period but the local data can be used repeatedly.

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The Domain Name System ● What it is to “Resolve”

Domain Names and IP Addresses

Iterative Lookup ● Alice’s computer does it all

Recursive Lookup ● A server does it all

Hijacking a query

Tracking your queries

Secure DNS Server

DNS Filtering

Matryoshka DNS Server