DNS Explained in 100 Seconds

Summary

The Domain Name System (DNS) functions like the internet's phone book, translating human-readable URLs into server IP addresses. When you enter a URL, the browser first checks the cache, then sends a DNS query to a recursive resolver. This resolver navigates through various DNS servers, starting with the root server and ending with the authoritative name server, to retrieve the IP address. DNS records include A records for IP mapping, CNAME for forwarding, MX for email, and TXT for additional data. The entire process occurs within a fraction of a second.

Takeaways

• 🌐 DNS (Domain Name System) is like the internet's phone book, mapping human-readable URLs to IP addresses.
• 🔍 When you enter a URL, your browser makes a DNS query to find the associated IP address.
• 📂 DNS first checks the local cache (browser or OS), and if it's empty, it uses a DNS recursive resolver.
• 🔁 A recursive resolver contacts multiple servers, starting with the root name server, then the top-level domain (TLD) server.
• 🗝 The final source of truth is the authoritative name server, which provides the requested website's IP address.
• ⏱️ Although the process seems complex, it happens within a fraction of a second.
• 🔗 Registering a domain name involves an accredited registrar, and your DNS settings are stored by a registry operator.
• 📝 Each domain has a zone file where DNS settings are configured, including the startup authority (SOA) record.
• 🏠 The A record maps a domain to an IP address, while CNAME records forward a domain to another domain.
• 📧 MX records are used for email, TXT records store arbitrary data, and NS records point to the name servers for a domain.

Q & A

What is the role of DNS in the internet?

DNS (Domain Name System) acts as the phone book of the internet. It maps human-readable URLs or hostnames, like www.fireship.io, to the IP address of the server hosting that site.

What happens when a URL is typed into a browser?

When a URL is entered into a browser, it makes a DNS query to find the IP address associated with that hostname. The browser first checks its local cache, and if the cache is empty, it sends a query to the DNS recursive resolver.

What is a DNS recursive resolver?

A DNS recursive resolver is a server responsible for looking up IP addresses by making multiple requests to other servers, starting with the root name server and working through to the authoritative name server.

Why is the resolver called 'recursive'?

The resolver is called 'recursive' because it must make multiple queries to different DNS servers, starting from the root server to the top-level domain (TLD) server, and finally the authoritative name server.

What is the role of the root name server in DNS resolution?

The root name server responds with the address of a top-level domain (TLD) DNS server, which stores data about TLDs like .com or .io. It helps the DNS resolver find the correct TLD server.

What is an authoritative name server?

An authoritative name server contains the final source of truth for a domain's IP address. It responds to the DNS resolver with the correct IP address for the requested website.

What is a zone file in DNS, and what does it contain?

A zone file is assigned to a domain registrant and contains the domain’s DNS settings. It includes records such as A records (for mapping domains to IP addresses), MX records (for email), and NS records (for name servers).

What is an A record in DNS?

An A record stands for 'Address' and maps a domain or subdomain to the IP address of its host, allowing users to access the website.

What is a CNAME record, and when is it used?

A CNAME (Canonical Name) record is used to forward a domain to another domain on the internet instead of pointing directly to an IP address.

Why are there usually two NS (name server) records for a domain?

There are usually two NS records for a domain to provide better reliability, ensuring that if one name server fails, the other can still handle DNS queries.