DNS

Intro

Domain Name System is the most well-known lookup service. A lookup service is something that maps domain names (google.com) to IP addresses.

DNS Namespaces

The parts of a url (the bits separated by full stops) roughly map to DNS servers, which exist in a heirarchy. Here's an example:

Root DNS Servers

Root servers are the first point of contact for a DNS query. This redirects the query to a top-level domain (TLD), such as .io or .com. There are somewhere around 2000 instances of root servers around the world, operated by 12 different organisations - see https://root-servers.org for more info.

Local DNS Cache

• DNS mappings are often cached locally to save time.
• This is done using a local resolver library, which is part of the OS.
• The local resolver library automatically makes a call to a local DNS server if the requested query is not cached.