How DNS Translates Domain Names to IP Addresses: A Complete Guide

1. What is DNS

DNS (Domain Name System) is an internet service that translates domain names to IP addresses.

It acts as a translator, converting a domain name into its corresponding IP address.

IP address: a numeric identifier that uniquely marks a computer on a network.

Domain name: a human‑readable, dot‑separated name identifying a computer or group of computers on the Internet.

2. Domain hierarchy

Domain names have a hierarchical structure: root domain, top‑level domain (TLD), second‑level domain, third‑level domain, etc.

Example: www.xxx.com – “www” is the third‑level domain, “xxx” the second‑level domain, and “com” the top‑level domain. The trailing dot represents the root domain and is usually omitted.

Each level is served by a domain name server.

3. Query methods

DNS queries can be performed in two ways:

Recursive query – the server must return the final answer to the requester.

Iterative query – the server points the requester to another server that may have the answer.

4. Caching

During resolution, DNS caches the mapping between domain names and IP addresses.

Browser cache – stores IP addresses after a page is visited.

Operating‑system cache – stored in the hosts file or OS DNS cache.

5. Resolution process

The step‑by‑step resolution flow:

Check the browser’s DNS cache.

If not found, check the OS DNS cache.

If still missing, the OS sends the query to the local DNS server, which may use its own cache.

If the local server lacks the answer, it performs an iterative query to the root server.

The root server returns the address of the appropriate TLD server.

The TLD server returns the authoritative name server for the domain.

The authoritative server returns the final IP address.

The local server caches the result and returns the IP to the OS, which caches it for the browser.

These steps are illustrated in the following diagrams:

6. DNS resource record types

Common DNS record types include: A – maps a domain to an IPv4 address. NS – specifies authoritative name servers for a zone. CNAME – alias record pointing to another domain name. SOA – start of authority, indicates the primary name server for a zone. PTR – reverse lookup, maps an IP address to a domain name. MX – mail exchange, designates mail servers for a domain. TXT – arbitrary text information associated with a domain. AAAA – maps a domain to an IPv6 address.