Networking Fundamentals Advanced +250 XP

DNS

The DNS Hierarchy & Namespaces

The Domain Name System (DNS) is the phone book of the internet. It maps human-readable hostname strings (e.g. devknow.com) into machine-routable IP addresses (e.g. 104.21.32.185).

Rather than a centralized table, DNS is structured as an absolute **hierarchical database tree** divided into zones managed by different authorities:

  • Root Servers (.): The absolute apex of the tree. There are 13 logical root server nodes globally, guiding queries to specific TLD registers.
  • Top-Level Domains (TLDs): Registry nodes representing suffixes like .com, .net, or .org.
  • Authoritative Nameservers: The final authority that holds the actual DNS records mapping specific domains to destination IPs.

Resolution Flow: Recursive vs Iterative

When you type a URL, your browser performs a DNS resolution sequence consisting of two query methods:

1. Recursive Query: Your client asks its local resolver (e.g., 8.8.8.8) to fetch the answer. The resolver assumes the complete burden of traversing the internet to return the final mapping.
2. Iterative Queries: The resolver queries the Root, which replies with the TLD. The resolver then queries the TLD, which points to the Authoritative server. Finally, the resolver queries the Authoritative Nameserver to get the raw IP.

Primary DNS Record Types

Every zone file contains standard DNS resource records. Knowing their layouts is vital for cloud engineering:

  • A Record: Maps a hostname to a 32-bit IPv4 address (e.g., 192.168.1.1).
  • AAAA Record: Maps a hostname to a 128-bit IPv6 address.
  • CNAME (Canonical Name): Maps an alias name directly to another domain name (useful for CDNs).
  • MX (Mail Exchanger): Specifying mail delivery servers, prioritised by numbers.
  • TXT Record: Holds arbitrary text (used heavily for SPF/DKIM security checks).