Understanding IP Subnetting and Masks

Aug 6, 2024

Lecture on IP Subnetting and Subnet Masks

Introduction

  • Understanding subnet masks is crucial in learning IP subnetting.
  • Differences between Class A, Class B, and Class C IP subnets are often discussed.
  • Classful subnetting architecture is outdated since 1993, today we use classless subnetting.
  • Reviewing classful subnetting helps in understanding modern subnetting.

IP Address Classes

  • Five Classes: A, B, C, D, E
    • Class A: 1-127 (for workstations)
    • Class B: 128-191 (for workstations)
    • Class C: 192-223 (for workstations)
    • Class D: 224-239 (for multicast)
    • Class E: 240-254 (reserved, not used in production)

Determining IP Address Class

  • Class A: First octet 1-127
  • Class B: First octet 128-191
  • Class C: First octet 192-223
  • Class D: First octet 224-239 (multicast)
  • Class E: First octet 240-254 (reserved)
  • Binary Conversion: First four bits help to determine the class
    • 0xxx: Class A
    • 10xx: Class B
    • 110x: Class C
    • 1110: Class D
    • 1111: Class E

Default Subnet Masks

  • Class A: 255.0.0.0
  • Class B: 255.255.0.0
  • Class C: 255.255.255.0
  • Class D and E: Not used for subnetting

Practical Examples

  • Example 1: IP Address 17.22.90.7
    • Class A
    • Network Address: 17.0.0.0
    • First Usable Host: 17.0.0.1
    • Broadcast Address: 17.255.255.255
    • Last Usable Host: 17.255.255.254
  • Example 2: IP Address 220.10.77.40
    • Class C
    • Network Address: 220.10.77.0
    • First Usable Host: 220.10.77.1
    • Broadcast Address: 220.10.77.255
    • Last Usable Host: 220.10.77.254
  • Example 3: IP Address 165.245.0.1
    • Class B
    • Network Address: 165.245.0.0
    • First Usable Host: 165.245.0.1
    • Broadcast Address: 165.245.255.255
    • Last Usable Host: 165.245.255.254

Calculating Key Values

  • Network Address: First IP in a subnet, set all host bits to 0
  • First Usable Host Address: Network address + 1
  • Broadcast Address: Last IP in a subnet, set all host bits to 1
  • Last Usable Host Address: Broadcast address - 1

Advanced Examples

  • Example 1: IP Address 10.74.222.11 (Class A)
    • Network Address: 10.0.0.0
    • First Usable Host: 10.0.0.1
    • Broadcast Address: 10.255.255.255
    • Last Usable Host: 10.255.255.254
  • Example 2: IP Address 172.16.88.200 (Class B)
    • Network Address: 172.16.0.0
    • First Usable Host: 172.16.0.1
    • Broadcast Address: 172.16.255.255
    • Last Usable Host: 172.16.255.254
  • Example 3: IP Address 192.168.4.77 (Class C)
    • Network Address: 192.168.4.0
    • First Usable Host: 192.168.4.1
    • Broadcast Address: 192.168.4.255
    • Last Usable Host: 192.168.4.254

Conclusion

  • These calculations are simpler with classful subnetting but modern networks use classless subnetting.
  • Future lessons will cover classless subnetting calculations.