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How does the Domain Name System (DNS) work?

sobes.tech AI

Answer from AI

DNS (Domain Name System) is a distributed system that translates domain names (e.g., example.com) into IP addresses (e.g., 192.0.2.1). It acts as the internet's phone book.

The process of translating a domain name into an IP address involves several steps:

  1. Client request: The user enters a domain name into the browser.
  2. Local DNS resolver: The browser sends a request to the local DNS resolver (usually configured in the operating system or router).
  3. Resolver cache: The resolver first checks its local cache. If the record is found, the IP address is returned directly to the client.
  4. Request to root server: If not found in cache, the resolver sends a request to the root DNS servers.
  5. Redirect to TLD server: The root server does not know the IP address of the requested domain but knows the IP addresses of the top-level domain (TLD) servers (e.g., .com, .org). It redirects the resolver to the appropriate TLD server.
  6. Redirect to authoritative server: The TLD server knows which authoritative DNS servers respond for the specific domain (e.g., example.com). It redirects the resolver to the authoritative server for the domain.
  7. Get IP address: The authoritative DNS server holds the records for the requested domain, including the IP address. It returns the IP address to the resolver.
  8. Caching and response to client: The resolver caches the obtained IP address (according to the record's TTL) and sends it back to the client.

Main components of DNS:

  • DNS resolver: The client-side component that initiates requests.
  • Root name servers: 13 clusters of servers worldwide that know the addresses of TLD servers.
  • TLD servers: Servers responsible for top-level domains (.com, .org, .ru, etc.), knowing the addresses of authoritative servers for each domain in their zone.
  • Authoritative name servers: Servers that store the actual DNS records for a specific domain.

Types of DNS records:

  • A (Address): Maps a domain name to an IPv4 address.
  • AAAA (IPv6 Address): Maps a domain name to an IPv6 address.
  • CNAME (Canonical Name): Creates an alias for another domain name.
  • MX (Mail Exchanger): Indicates mail servers responsible for receiving mail for the domain.
  • TXT (Text): Used to store textual information (e.g., for SPF, DKIM).
  • NS (Name Server): Indicates authoritative DNS servers for the domain.

Example zone record:

// A record for the main domain
@ IN A 192.0.2.1
// CNAME record for subdomain www
www IN CNAME @
// MX record (priority 10)
@ IN MX 10 mail.example.com.
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