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N&SA-2025-S1-Wk3-2

Domains and Subdomains

  • Domain Hierarchy: A domain can have multiple subdomains, creating a hierarchical structure.

    • acmebw.com is the main domain.
    • Subdomains like sales.acmebw.com exist.
    • Domains can extend to the fourth level or more, each being unique.

  • Subdomain Definition: A domain is a subdomain of another if its root node is a descendant of the other's root node.

    • Example: sales is a subdomain of acmebw.com.

  • Example Breakdown: cannabis.uti.82.ac.nz illustrates subdomain structure.

    • cannabis is a subdomain of uti.82.ac.nz.

  • Email Access Example: Accessing email might involve a subdomain.

    • mail.82.ac.nz or staff.82.ac.nz, where mail or staff is the subdomain.
    • The structure is: subdomain (level four) to level three, to level two, up to the main domain.

Root of DNS

  • Coherent Namespace: The root of the Domain Name System (DNS) provides a coherent, consistent namespace using a single root in a hierarchical tree structure.
  • Uniqueness: This root holds definitions for all top-level domains, ensuring each is unique.
    • There can only be ONE, guaranteeing uniqueness.
  • Inconsistency Issues: Violating this rule leads to inconsistency, potentially directing users to the wrong domain.
    • This is a method criminals use to steal information.

Domain Registration

  • Guarantee of Uniqueness: Registering a domain name properly ensures that only one exists, and it belongs to the registrant.

DNS Name Servers

  • Limited Number: Due to protocol limitations, there are only 13 root name servers worldwide.
    • Their primary job is to manage the root.

RFCs and Top-Level Domain Structure

  • RFC 881 and RFC 920: These documents detail the concept of functional domains.

    • .com for commercial enterprises.
    • .edu for education.
    • .gov for government.

  • RFC 920: It also provided for country domains.

  • Stability: The top-level domain structure remained stable until around 1997 (covered later).

Current Top-Level Domains

  • Generic Domains:

    • .com
    • .net
    • .org

  • Country Codes: Top-level domains include country codes.

    • .af for Afghanistan
    • .nz for New Zealand
    • .eu for Australia
    • .al for Albania
    • .dz for Algeria

  • Domain International: For international treaty organizations.

U.S. Legacy Top-Level Domains

  • Governmental Organizations: .gov
  • Military: .mil
  • Educational Institutions: .edu

Country-Specific Government Domains

  • Specific Setups: Countries like Australia and New Zealand use specific setups to denote government domains.
    • New Zealand Government: .govt.nz
    • Australia: .gov.au