Understanding DNS Domain Name Resolution and Its Process

DNS (Domain Name System) translates human‑readable domain names into IP addresses, enabling computers to locate each other on the Internet.

IP addresses are numeric identifiers for computers, but they are hard to remember, so domain names were introduced as a more user‑friendly symbolic representation.

Since computers can only process numeric IP addresses, DNS performs the translation from domain names to IP addresses.

DNS Resolution Process

When a user enters a URL such as www.baidu.com , the resolution typically involves about ten steps, starting with local cache checks and ending with queries to authoritative name servers.

Step 1 : The browser checks its own cache for a previously resolved IP address.

Step 2 : If not found, the operating system’s cache (e.g., /etc/hosts on Linux or C:\Windows\System32\drivers\etc\hosts on Windows) is consulted.

Step 3 : The request is sent to the configured local DNS server.

Step 4 : If the local DNS server still lacks the answer, it queries a root DNS server.

Step 5 : The root server returns the address of the appropriate top‑level domain (TLD) server (e.g., .com, .cn).

Step 6 : The local DNS server queries the TLD server.

Step 7 : The TLD server returns the authoritative name server for the domain.

Step 8 : The authoritative name server provides the final IP address and TTL.

Step 9 : The local DNS server caches the result according to the TTL.

Step 10 : The IP address is returned to the client, completing the resolution.

Recursive vs. Iterative Queries

In recursive resolution, the local DNS server performs all subsequent queries on behalf of the client until it obtains the final answer.

In iterative resolution, the client contacts each server in turn, receiving referrals until it reaches the authoritative server.

Common DNS Record Types

A : Maps a domain name to an IPv4 address.

MX : Directs email for a domain to a mail server.

CNAME : Provides an alias for another domain name.

NS : Specifies the authoritative name servers for a domain.

TXT : Holds arbitrary text information, often used for verification.