Why DNS Changes Don't Update Instantly: The Role of Caching and TTL

When a DNS record is updated, the change does not instantly reflect across the internet because millions of systems rely on cached DNS information. DNS is stored in multiple layers of cache, including browsers, operating systems, routers, ISPs, and recursive resolvers like Google's 8.8.8.8 and Cloudflare's 1.1.1.1. There is no global mechanism that pushes DNS updates to every network simultaneously; instead, old cached answers simply expire before resolvers fetch the new ones. The delay most users experience during so-called 'DNS propagation' is therefore a caching problem, not a distribution problem. Three key concepts — DNS cache, TTL (Time to Live), and recursive resolvers — determine how long outdated DNS answers persist across the internet.