The Domain Name System

Nobody types 203.0.113.40 to open a link; they type hop.example. Computers, however, connect to numbers. The Domain Name System (DNS) is the internet's phone book that turns one into the other — and it is the first step of every single request Hop receives.

The rule

Ask down the chain once, then trust the cache until TTL.

When a browser needs hop.example, it checks its own cache, then the operating system's. If neither knows, it asks a recursive resolver (usually run by the internet provider or a public service), which walks the chain for it:

1. Root servers — "for .example, ask these servers".
2. TLD servers for .example — "for hop.example, ask Hop's name servers".
3. Authoritative name servers for hop.example — "it is 203.0.113.40".

Each answer carries a TTL (time to live) in seconds. Every cache along the way keeps the answer until the TTL runs out, so the next visitor skips the whole walk.

Common record types:

Managed DNS services can also do routing: return different addresses by weight (send 10% to a new server), by the user's location, or only to servers that pass health checks.

The shortcut

Every TTL is a trade: long TTL = fast lookups, slow changes; short TTL = quick changes, more lookups. Before any change of address, shrink the TTL first.

The trap is forgetting that you control only your authoritative servers. Caches around the world keep old answers until the TTL they were given runs out — you cannot flush them.

Drills

Answer fast — trust the rule.

Remember

• Ask down the chain once — root, TLD, authoritative — then trust the cache until TTL.
• Shortcut: long TTL = fast lookups, slow changes; shrink it before any move.
• Trap: you cannot flush other people's caches; they keep old answers until the TTL runs out.