DNS: ментальная модель

Question

Accepted Answer

DNS — phone book: name → IP via hierarchical cached lookup. Almost every answer from cache, not full tree walk.

## Разбор

Browser needs IP, not `example.com`. **Resolution** — hierarchical, cached. Domain right-to-left tree:

```
                    . (root)
                    │
            ┌───────┴───────┐
           com             org        ← TLD servers
            │
        example.com                   ← authoritative server (owns the records)
            │
   www / api / mail ...               ← subdomains / records
```

Key insight: **almost every lookup answered from cache**. OS cache, **recursive resolver** (`1.1.1.1`/`8.8.8.8`), each honours **TTL**. Full walk only on true miss.

## Итог

DNS before first byte; TTL layers and prefetch/preconnect are front-end perf levers.