DNS System — Simple

Problem statement (interviewer prompt)

Design the DNS system: a hierarchical, distributed name-resolution protocol mapping names to IPs (and more). Cover authoritative vs recursive resolvers, caching + TTLs, anycast for global availability, DNSSEC, and how a single name lookup actually flows end-to-end.

flowchart LR
  C([Client / OS resolver])
  RES[Recursive Resolver]
  ROOT[Root NS]
  TLD[TLD NS]
  AUTH[Authoritative NS]
  C --> RES --> ROOT
  RES --> TLD
  RES --> AUTH --> RES --> C

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class C client;
    class RES,ROOT,TLD,AUTH service;