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Definition
DNS (Domain Name System) is the internet's phone book. It translates human-readable domain names (like google.com) into IP addresses (like 142.250.80.46) that computers use to locate each other on the network.
When you type a URL into your browser, a DNS lookup occurs before any web content loads. Your device first checks its local cache, then queries a recursive resolver (usually provided by your ISP or a public service like 1.1.1.1 or 8.8.8.8). The resolver walks the DNS hierarchy: root servers point to TLD servers (.com, .org), which point to the domain's authoritative name servers, which return the actual IP address. This entire process typically completes in under 100 milliseconds.
DNS stores more than just IP addresses. A records map domains to IPv4 addresses. AAAA records map to IPv6. CNAME records create aliases (www pointing to the bare domain). MX records direct email to mail servers. TXT records store arbitrary text, used for email authentication (SPF, DKIM, DMARC) and domain verification. NS records delegate DNS authority to specific name servers.
DNS lookup time directly affects page load speed. Slow DNS adds latency to every new domain your page references (fonts, analytics, CDN assets). Strategies to minimize DNS impact include using a fast DNS provider, reducing the number of external domains a page references, DNS prefetching (via the dns-prefetch link tag), and keeping TTL (time-to-live) values appropriately balanced between freshness and caching efficiency.