DNS: The Internet's Phone Book
How names become addresses
How names become addresses
Type a domain name and watch the DNS lookup happen step by step. Your query travels through multiple servers before getting an answer.
A DNS zone contains records that map names to values. Different record types serve different purposes. Click each type to see what it does.
When a resolver gets an answer, it caches it for the TTL duration. Higher TTL = fewer lookups but slower propagation of changes. Drag the slider to see the trade-off.
DNS is one of the most critical pieces of internet infrastructure.
Before your browser can connect to any website, it must resolve the domain name to an IP. This DNS lookup adds 20-100ms to every first visit.
When you send email to user@gmail.com, your mail server looks up the MX record for gmail.com to find Google's mail servers. Without MX records, email cannot work.
DNS can point to backup servers. If your primary goes down, update the A record to point to a backup. With low TTL, traffic shifts within minutes.
The entire DNS system is run by 13 root server clusters (labeled A through M). Each "server" is actually hundreds of machines distributed globally using anycast routing. They handle over 10 billion queries per day and have never all gone down simultaneously.
You've learned how domain names translate to IP addresses, how DNS records control where traffic goes, and how caching makes it all fast. Every website visit starts with a DNS lookup.
Humans remember names (google.com). Computers need numbers (142.250.80.46). DNS translates between them, like a phone book for the internet.
A records point to IPv4 addresses. CNAME records are aliases (www points to the main domain). MX records route email. Each type serves a different purpose.
Time To Live tells resolvers how long to cache a result. High TTL (86400s) = fewer lookups but slow changes. Low TTL (60s) = fast changes but more lookups.
Your query goes: browser cache, OS cache, router, ISP resolver, root server, TLD server (.com), authoritative server. Each level narrows the search.
Put your new knowledge into practice!