Lecture on IP Version 4 and IP Address Classes

Introduction to IP Address Classes

• IP addresses in version 4 are often referred to by classes (Class A, B, C).
• Classes describe an IP address in relation to its subnet mask.
• Although class-based subnetting hasn't been used since 1993, the terminology persists.

Class-Based Addressing

• Class A:
  • 8 bits for network, 24 bits for host.
  • Default subnet mask: 255.0.0.0.
• Class B:
  • 16 bits for network, 16 bits for host.
  • Default subnet mask: 255.255.0.0.
• Class C:
  • 24 bits for network, 8 bits for host.
  • Default subnet mask: 255.255.255.0.

Purpose of Class-Based Networking

• Classes provide a starting point for subnetting networks.
• Each class clearly demarcates the network and host parts of an IP address.

IP Address Classes and Their Ranges

• Class A:
  • First octet range: 0-127
  • Binary: First bit is 0
• Class B:
  • First octet range: 128-191
  • Binary: First two bits are 10
• Class C:
  • First octet range: 192-223
  • Binary: First three bits are 110
• Class D:
  • Used for multicast, range: 224-239
  • Binary: First four bits are 1110
• Class E:
  • Reserved range: 240-255
  • Binary: First four bits are 1111

Class Identification Examples

• 17.X.X.X: Class A
• 220.X.X.X: Class C
• 165.X.X.X: Class B
• 128.X.X.X: Class B
• 192.X.X.X: Class C

Calculating Subnet Values

• Important Values:
  • Network address: Set all host bits to 0.
  • First usable host address: Network address + 1.
  • Network broadcast address: Set all host bits to 1.
  • Last usable host address: Broadcast address - 1.

Example Calculations

• IP 10.74.22.11:
  • Class A: Network address 10.0.0.0, First host 10.0.0.1, Broadcast 10.255.255.255, Last host 10.255.255.254.
• IP 172.16.188.200:
  • Class B: Network address 172.16.0.0, First host 172.16.0.1, Broadcast 172.16.255.255, Last host 172.16.255.254.
• IP 192.168.4.91:
  • Class C: Network address 192.168.4.0, First host 192.168.4.1, Broadcast 192.168.4.255, Last host 192.168.4.254.

Subnetting Process

• The class system serves as a foundational guide for subnetting.
• The process is consistent for both class-based and non-class-based IPs and subnet masks.