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knowledge/technology/internet/DNS.md
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2024-06-02 20:43:53 +02:00

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concept https://de.wikipedia.org/wiki/Domain_Name_System https://datatracker.ietf.org/doc/html/rfc1034 2024-03-14

Domain Name System

The Domain Name System (DNS) is a hierarchical and distributed naming system that translates human-readable domain names into IP addresses, facilitating the mapping of hostnames to IP addresses on the internet. DNS plays a crucial role in making web browsing and various internet services accessible by allowing users to interact with websites using easy-to-remember domain names instead of numeric IP addresses.

Components of DNS

1. Domain Name Space:

  • Root Domain: The highest level of the hierarchy represented by a dot (.). It is managed by the Internet Assigned Numbers Authority (IANA).
  • Top-Level Domains (TLDs): Immediately below the root, examples include .com, .org, .net.
  • Second-Level Domains (SLDs): Situated directly beneath TLDs, these are often used to identify specific entities or organizations.
  • Subdomains: Further subdivisions of domains, creating a hierarchical structure (e.g., blog.example.com).

2. DNS Servers:

  • Root DNS Servers: Initially contacted to resolve any domain. They provide information about the authoritative DNS servers for each TLD.
  • TLD DNS Servers: Responsible for handling queries related to specific top-level domains.
  • Authoritative DNS Servers: Hold the actual DNS records for a domain and provide the authoritative answers.
  • Recursive DNS Servers: These servers query other DNS servers on behalf of a client until a complete answer is obtained.

3. DNS Records:

  • A (Address) Record: Maps a domain to an IPv4 address.
  • AAAA (IPv6 Address) Record: Maps a domain to an IPv6 address.
  • CNAME (Canonical Name) Record: Alias of one domain to another.
  • MX (Mail Exchange) Record: Specifies mail servers responsible for receiving email.
  • NS (Name Server) Record: Indicates authoritative DNS servers for the domain.

DNS Resolution Process

  1. User Input: A user enters a domain name into a web browser.
  2. Local DNS Resolver: The user's device queries a local DNS resolver (usually provided by the ISP).
  3. Recursive Query: If the local resolver doesn't have the information, it recursively queries the root DNS servers, then TLD servers, and finally the authoritative DNS server for the specific domain.
  4. Response: The authoritative DNS server responds with the IP address associated with the requested domain.
  5. Caching: The resolved IP address is cached at various levels to speed up future requests for the same domain.

DNS Security

DNS plays a crucial role in internet security, and various measures are in place to protect against attacks, including:

  • DNSSEC (DNS Security Extensions): Provides data integrity and authentication for DNS responses, preventing DNS spoofing.
  • DNS Filtering: Blocks access to malicious websites by filtering DNS queries based on predefined policies.

Using DNS

DNS traditionally operates over both UDP and TCP, with UDP being the default choice for standard query/response operations on port 53

DNS over HTTPS (DoH)

DoH uses the HTTPS protocol (Port 443/tcp) to encapsulate DNS queries. This makes it very secure and hard to block on a firewall level.

DNS over TLS (DoT)

DoT uses TLS encryption for DNS queries and runs on port 853/tcp

Common DNS Servers

  • 1.1.1.1, https://dns.cloudflare.com/dns-query - Cloudflare DNS
  • 8.8.8.8, https://dns.google/dns-query - Google DNS
  • https://doh.mullvad.net/dns-query - Mullvad DNS over HTTPs