👁️ View Presentation ⬇️ Download PPT
Complete Guide to Domain Name System (DNS)

Complete Guide to Domain Name System (DNS)

Table of Contents

Introduction to DNS

The Domain Name System (DNS) is a fundamental component of the internet that translates human-friendly domain names into machine-readable IP addresses. It functions as a distributed directory service that maintains a mapping between hostnames and their numerical addresses.

How DNS Works

When you enter a domain name in your browser (e.g., www.example.com), a DNS client (resolver) sends a request to a DNS server to find the corresponding IP address. The DNS server either provides the answer directly or queries other servers to find the information.

DNS is essential because while humans find names easier to remember, network devices require IP addresses to route traffic. This system bridges the gap between human convenience and network requirements.

Name Space Organization

DNS organizes names in a structured way to ensure uniqueness and efficient resolution. There are two primary approaches to organizing name spaces:

1. Flat Name Space

In a flat name space:

  • Names are assigned to addresses without any hierarchical structure
  • Each name is a sequence of characters without inherent meaning
  • Requires centralized control to prevent duplication

Flat name spaces are impractical for large systems like the Internet due to the need for centralized control and the difficulty of maintaining uniqueness at scale.

2. Hierarchical Name Space

In a hierarchical name space:

  • Names are composed of multiple parts with specific meanings
  • Authority can be decentralized (e.g., different organizations manage different parts)
  • Enables scalability for large networks like the Internet

The hierarchical approach is what DNS uses, with names like mail.google.com where:

  • com is the top-level domain (TLD)
  • google is the second-level domain
  • mail is the subdomain or hostname

Domain Name Space

The DNS hierarchical name space is structured as an inverted tree with up to 128 levels (0-127), where level 0 is the root.

[Diagram of DNS tree structure would appear here]

Key Components

Labels

Each node in the tree has a label:

  • Maximum of 63 characters
  • Root label is empty (null string)
  • Siblings must have unique labels

Domain Names

A domain name is the sequence of labels from a node to the root, separated by dots:

  • Read from left (specific) to right (general)
  • Technically ends with a null label (implied dot)
  • Example: mail.google.com. (the trailing dot represents the root)

Fully Qualified vs. Partially Qualified

Type Description Example
FQDN (Fully Qualified Domain Name) Complete name ending with root (dot) mail.google.com.
PQDN (Partially Qualified Domain Name) Incomplete name, resolver adds suffix mail (resolver might add .google.com)

Domains

A domain is a subtree of the name space:

  • Can be divided into subdomains
  • Example: google.com is a domain that contains subdomains like mail.google.com

Distribution of Name Space

The DNS information is distributed across many servers worldwide for efficiency and reliability.

Hierarchy of Name Servers

The DNS hierarchy is mirrored by a hierarchy of servers:

  • Root servers (top of hierarchy)
  • Top-level domain (TLD) servers (e.g., .com, .org)
  • Authoritative servers (for specific domains)

Zones

A zone is a contiguous portion of the domain name space that a server is responsible for:

  • May be an entire domain or part of one
  • Each zone has a zone file containing its information

Server Types

Server Type Description
Root Server Knows about TLD servers, delegates authority
Primary Server Maintains and updates zone files
Secondary Server Gets zone data from primary servers for redundancy

DNS in the Internet

The Internet's domain name space is divided into three main sections:

1. Generic Domains

Define registered hosts by their generic behavior:

Label Purpose
.com Commercial organizations
.edu Educational institutions
.gov Government agencies
.org Non-profit organizations
.net Network infrastructure

2. Country Domains

Use two-letter country codes (e.g., .us, .uk) with possible subdivisions:

  • Example: anza.cup.ca.us → De Anza College in Cupertino, California, USA

3. Inverse Domain

Used for reverse DNS lookups (IP address to name):

  • First-level node: arpa
  • Second-level node: in-addr
  • IP addresses are reversed (e.g., 132.34.45.121 becomes 121.45.34.132.in-addr.arpa)

Name-Address Resolution

The process of mapping names to addresses (or vice versa) is called resolution.

Resolver

The DNS client that initiates queries is called a resolver.

Resolution Methods

1. Recursive Resolution

  • Resolver asks for complete answer
  • Server handles all intermediate queries
  • Returns final answer to resolver

2. Iterative Resolution

  • Server returns best answer it can
  • May refer resolver to other servers
  • Resolver must contact referred servers

[Diagram comparing recursive and iterative resolution would appear here]

DNS Messages

DNS uses two message types with identical formats:

Message Type Contents
Query Header + Question section
Response Header + Question + Answer + Authority + Additional sections

Header Format

12-byte header containing:

  • Identification (matches queries with responses)
  • Flags (message type, desired resolution type, etc.)
  • Counts for each section

Message Sections

Section Purpose
Question Contains the query (present in both message types)
Answer Response records (only in response messages)
Authority Information about authoritative servers (response only)
Additional Extra information that might help resolver (response only)

DNS Records

DNS uses two main record types:

1. Question Records

Used in the Question section to specify the query.

2. Resource Records

Contain the actual DNS data in responses. Types include:

Record Type Purpose
A IPv4 address
AAAA IPv6 address
CNAME Canonical name (alias)
MX Mail exchange
NS Name server
PTR Pointer (for reverse DNS)
SOA Start of authority
TXT Text information

Domain Registration

New domains are added through accredited registrars:

Registration Process

  1. Registrar verifies domain name uniqueness
  2. Enters domain into DNS database
  3. Requires server name and IP address

Example Registration

To register ws.wonderful.com:

  • Domain name: ws.wonderful.com
  • IP address: 200.200.200.5

ICANN Accreditation

Registrars must be accredited by the Internet Corporation for Assigned Names and Numbers (ICANN). A list of accredited registrars can be found at www.intenic.net.

Key Takeaways

  • DNS translates domain names to IP addresses and vice versa
  • Uses a hierarchical name space for scalability
  • Distributed across servers worldwide for reliability
  • Supports both forward (name→IP) and reverse (IP→name) lookups
  • New domains are registered through ICANN-accredited registrars