DNS Resolution

DNS Resolution

The Domain Name System (DNS) translates human-readable domain names into IP addresses. When you visit example.com, DNS resolves it to an IP like 93.184.216.34.

DNS Hierarchy

                  . (root)
                 / \
              .com  .org
              /       \
         example     mozilla
           |           |
          www         www

Record Types

Resolution Process

1. Client checks local cache
2. Query recursive resolver
3. Resolver queries root server -> TLD server -> authoritative server
4. Response cached and returned

Your Task

Implement a DNSResolver class that simulates DNS resolution:

• addRecord(domain, type, value) — adds a DNS record
• resolve(domain, type) — resolves a domain, following CNAME chains
• addToCache(domain, type, value, ttl) — adds to cache with TTL
• resolveWithCache(domain, type, currentTime) — resolves using cache (returns null if expired)