DNS Fundamentals

Domain Name System (DNS)

The Resolution Chain (Recursion)

1. Stub Resolver: Client OS. Checks local cache/hosts file.
2. Recursive Resolver: (e.g., 1.1.1.1). Performs the lookup on behalf of the client. Caches results aggressively. What is a Recursive DNS? (Cloudflare).
3. Root Server: Points to TLD servers (.com, .org).
4. TLD Server: Points to Authoritative Nameservers.
5. Authoritative Nameserver: Holds the actual records for the domain.

Record Types

• A / AAAA: Maps hostname to IPv4 / IPv6 address. DNS Record Types (Google Cloud).
• CNAME: Canonical Name. Maps hostname to hostname.
  • Limitation: Cannot exist at the root (@) of a zone (RFC 1034).
  • Cloudflare Solution: CNAME Flattening allows CNAMEs at the root by resolving them to IPs at the edge. CNAME Flattening (Cloudflare).
• MX: Mail Exchange. Priority-based routing for email.
• TXT: Arbitrary text. Used for verification (SPF, DKIM, Google Site Verification).
• NS: Delegated nameservers for the zone.
• SOA: Start of Authority. Zone parameters (serial number, refresh intervals).

Split-Horizon DNS

Serving different DNS answers depending on the source of the query (e.g., Internal users get Private IP, External users get Public IP).