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IP, Subnetting, DNS, DHCP

1 Global Definitions

  • IP Address: A unique numerical identifier assigned to devices on a network.
  • Subnetting: The practice of dividing a larger network into smaller, more manageable segments.
  • DNS (Domain Name System): Converts human-readable domain names into IP addresses.
  • DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses and configuration settings to devices on a network.

1.1 Internet Protocol (IP)

IPv4

32-bit addressing system widely used for decades.

  • Format: 192.168.1.1
  • Address space: ~4.3 billion addresses
  • Divided into classes

IPv6

128-bit addressing system designed to replace IPv4.

  • Format: 2001:0db8:85a3::8a2e:0370:7334
  • Provides ~340 undecillion addresses
  • Built-in IPsec

1.2 Subnetting

Subnet Masks

Define which portion of an IP address is the network and which is the host.

  • Example: 255.255.255.0 or /24
  • Separates network ID from host ID

Benefits of Subnetting

Improves network management and efficiency.

  • Reduces broadcast traffic
  • Enhances security by isolating groups
  • Optimizes IP address allocation

CIDR (Classless Inter-Domain Routing)

A flexible method of subnetting introduced to replace rigid class-based addressing.

  • Notation: /n (e.g., /16, /24)
  • Allows efficient IP allocation

1.3 Domain Name System (DNS)

How DNS Works

Translates domain names into IP addresses.

  • DNS Resolver
  • Root Servers
  • Authoritative DNS servers

DNS Records

Types of data stored in DNS entries.

  • A record → maps domain to IPv4
  • AAAA record → maps domain to IPv6
  • CNAME → canonical name (aliases)
  • MX → mail exchange

DNS Security

DNS is often targeted by attackers.

  • DNS Spoofing
  • DNS over HTTPS (DoH) for privacy

1.4 Dynamic Host Configuration Protocol (DHCP)

How DHCP Works

Automates assignment of IP addresses and network configurations.

  • DORA Process
  • Assigns IP, subnet mask, gateway, DNS

Benefits of DHCP

Simplifies network management and reduces manual errors.

  • Centralized control of IP assignments
  • Efficient re-use of IP addresses
  • Supports dynamic networks (e.g., Wi-Fi)

DHCP Security Concerns

Misuse of DHCP can compromise networks.

  • Rogue DHCP Servers
  • DHCP snooping as a mitigation

1.5 Why These Concepts Matter

IP, subnetting, DNS, and DHCP are the foundations of networking. Without them, devices cannot communicate effectively, scale securely, or connect to the wider internet. Security professionals must understand these fundamentals to configure secure environments, detect anomalies, and mitigate attacks.