Understanding DNS: Architecture, Hierarchy, and Servers

What is DNS?

DNS (Domain Name System) is a service responsible for translating IP addresses into domain names and vice versa. It follows a client-server architecture and consists of a massive distributed database managed by specialized software.

Hierarchical Structure of DNS

• Root DNS Server: There are 13 super-servers scattered globally that work in unison. They contain the master tables for name resolution, though most operational work is delegated to other servers.
• Top-Level Domains (TLD): Maintained by internet authorities, these resolve top-level domain names.
• Second-Level Domains: These resolve second-level domain names and are maintained by domain owners or Internet Service Providers (ISPs).
• Subdomains: Added to the left of the domain name, these are managed by the owner of the second-level domain.
• Host Name: Any system on the internet can have a host name added to the left of its domain name (e.g., www for a web server, ftp for file transfers).

Key DNS Terminology

A Fully Qualified Domain Name (FQDN) is the complete DNS name of a system, ranging from the host name to the top-level domain. Example: www.windows.microsoft.com

• Domain: A collection of domain names that share the same top-level and second-level domain names.
• Domain Name Space: The entire tree structure extending from the root to individual host names.
• Zone of Authority: The database or information set that defines rules for a specific domain or set of domains. This information is stored as records.

Types of DNS Servers

• Primary Server: Stores the database for an area locally. These must be maintained manually by an administrator and are used to resolve domain names.
• Secondary Server: Maintains copies of the databases stored on primary servers. They are configured to update automatically via periodic data dumps and also resolve domain names.
• Local Cache Servers: These connect to other servers to resolve client DNS requests. They do not resolve names themselves but maintain a cache of recent queries, which are cleared once outdated.

Reverse DNS Resolution

Reverse resolution involves determining the domain name from an IP address. This feature should be enabled on DNS servers, as it is often required for specific low-level network functions.