Neural Nets

DNS Architecture And DNS Records

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dns, dns records, computer networks

The Domain Name System (DNS) is a critical component of the internet infrastructure. It translates human-readable domain names into IP addresses that computers use to communicate. This article explores the architecture of DNS and the types of DNS records used to manage domain behavior and configuration.

Domain Name System Overview

DNS functions as a distributed, hierarchical system that enables efficient domain name resolution. Below is a breakdown of how DNS queries are handled from the user’s device to the final authoritative response.

1. Applications on the User’s Computer

  • Web browsers and email clients initiate DNS queries when accessing websites or sending emails.
  • These applications may maintain an application-specific DNS cache, which temporarily stores responses to reduce the need for repeated queries.

2. Local Resolver

  • The local resolver is typically part of the operating system and is the first point of contact for DNS queries.
  • It maintains a local cache to improve performance by storing recently resolved domain names, governed by a Time-To-Live (TTL) value.

3. Caching/Forwarding Resolver

  • Provided by the ISP or organization, this resolver manages a multi-user DNS cache.
  • If a domain is not found in the cache, the query is forwarded to an external resolver (e.g., Google DNS or Cloudflare).

4. Recursive Resolver

  • The recursive resolver performs a full DNS lookup by querying other servers in the DNS hierarchy.
  • It starts with the root server, then queries the appropriate top-level domain (TLD) server, and finally reaches the second-level domain (SLD) server to get the authoritative answer.

5. Authoritative DNS Servers

  • Root Server: Directs queries to TLD servers based on the requested domain extension.
  • TLD Server: Handles queries for specific domain extensions (e.g., .com, .org).
  • SLD Server: Contains the DNS records for individual domains and returns the final response (such as an IP address).

DNS Records Overview

DNS records define how a domain behaves by mapping names to IP addresses, email servers, services, and more. Each record type has a specific structure and purpose.

1. DNS Meta Records

  • NS (Name Server): Defines the authoritative servers for a domain.
  • SOA (Start of Authority): Contains administrative details like primary server, contact email, serial number, and caching parameters.
  • CNAME (Canonical Name): Creates an alias for another domain.
  • PTR (Pointer): Used in reverse DNS lookups (IP to domain).
  • DNAME (Delegation Name): Redirects an entire domain subtree to another domain.
  • OPT (Option): Extends DNS functionality (part of EDNS), enabling larger packets and additional features.

2. IP Address Records

  • A Record: Maps a domain to an IPv4 address.
  • AAAA Record: Maps a domain to an IPv6 address.
  • APL (Address Prefix List): Defines lists of IP prefixes, used for advanced routing or policy systems.

3. Informational Records

  • TXT (Text Record): Holds arbitrary text, often used for domain verification, SPF, or DKIM records.
  • HINFO (Host Information): Describes the system’s hardware and OS (seldom used).
  • LOC (Location): Provides geolocation data for the domain.
  • RP (Responsible Person): Lists the contact for the domain administrator.

4. Service Discovery Records

  • SRV (Service Record): Specifies the location and port of services like VoIP or LDAP.
  • NAPTR (Naming Authority Pointer): Works with SRV to support complex service discovery, using pattern-based rules.
  • MX (Mail Exchange): Directs email to mail servers for the domain.
  • SMIMEA (S/MIME Association): Associates S/MIME certificates with email addresses for secure communication.

6. Security Records

  • DNSKEY: Public key used for signing DNS records in DNSSEC.
  • RRSIG (Resource Record Signature): A cryptographic signature for DNSSEC records.
  • NSEC / NSEC3: Used to prove nonexistence of DNS records.
  • DS (Delegation Signer): Links child zone signatures to parent zones in DNSSEC.
  • TLSA: Associates TLS certificates with a domain (used with DANE).
  • SSHFP (SSH Fingerprint): Stores SSH public key fingerprints.
  • CAA (Certification Authority Authorization): Restricts which certificate authorities can issue certificates for a domain.

7. Miscellaneous Records

  • URI (Uniform Resource Identifier): Stores a URI for services associated with the domain.
  • SVCB / HTTPS: Modern alternatives to SRV records for secure service discovery.
  • AFSDB (Andrew File System Database): Maps domains to AFS database servers (rarely used).
  • EUI48 / EUI64: Stores MAC addresses for device identification.

Conclusion

DNS is a foundational system that enables seamless communication across the internet by resolving domain names into machine-friendly addresses. Understanding DNS architecture and record types is essential for configuring domains, securing services, and optimizing network performance. From basic A records to advanced DNSSEC configurations, each record plays a role in shaping how users and applications interact with online resources.