What is DNS?

DNS — the Domain Name System — is the internet's phonebook. It translates domain names like toolcrux.com into the IP addresses that computers use to connect to servers.

Definition

When you type a domain into a browser, your computer doesn't know the IP address of the server. DNS resolves this by querying a hierarchy of servers that together map domain names to IP addresses.

Common DNS Record Types

  • A — maps a domain to an IPv4 address (e.g. 93.184.216.34)
  • AAAA — maps a domain to an IPv6 address
  • CNAME — creates an alias from one domain to another
  • MX — specifies mail servers for the domain
  • TXT — stores arbitrary text, commonly used for domain verification and SPF/DKIM records
  • NS — specifies the authoritative nameservers for the domain
  • SOA — Start of Authority, contains administrative information about the zone

How DNS Resolution Works

  1. You type toolcrux.com into your browser.
  2. Your computer checks its local cache. If the record is there and hasn't expired, it uses it.
  3. If not cached, it asks your ISP's recursive resolver.
  4. The resolver queries the root nameservers to find who handles .com.
  5. The resolver then queries the .com registry to find ToolCrux's authoritative nameservers.
  6. The resolver asks the authoritative nameserver for the A record and gets the IP address.
  7. The IP is returned to your browser, which makes the HTTP connection.

What is TTL?

TTL (Time to Live) is the number of seconds a DNS record can be cached before it must be re-fetched. A low TTL (e.g. 300 seconds) means changes propagate quickly. A high TTL (e.g. 86400 = 24 hours) reduces DNS query load but means changes take longer to spread.

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Frequently Asked Questions

What is DNS propagation?

DNS propagation is the time it takes for updated records to spread to all DNS servers worldwide. It depends on the TTL set on the records and can take minutes to 48 hours.

What is the difference between DNS and WHOIS?

DNS maps a domain to an IP address. WHOIS tells you who owns the domain. DNS is about routing; WHOIS is about ownership.

What is a DNS resolver?

A DNS resolver (also called a recursive resolver) is a server that performs the full DNS lookup process on behalf of your device. Your ISP provides one by default; you can also use public resolvers like 1.1.1.1 (Cloudflare) or 8.8.8.8 (Google).

Related Terms

  • WHOIS — Domain ownership and registration data.
  • SSL/TLS — Encryption that secures the connection once DNS resolves.
  • HTTP Headers — The metadata exchanged once a DNS-resolved connection is made.