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CCNA Subnetting Essentials and Techniques

May 19, 2025

Jeremy's IT Lab: CCNA Subnetting Lecture

Introduction

  • Free course for CCNA.
  • Importance of subnetting for network engineers and CCNA exam.
  • Subnetting tutorial split into 2-3 videos for clarity.
  • Simplicity emphasized, avoiding over-complication.

Topics Covered

  1. CIDR (Classless Inter-Domain Routing)

    • Introduces flexibility in IPv4 addressing compared to traditional class A, B, C.
  2. IPv4 Address Classes Review

    • Class A:
      • First octet begins with 0, range 0-127.
      • /8 prefix length.
    • Class B:
      • First octet begins with 10, range 128-191.
      • /16 prefix length.
    • Class C:
      • First octet begins with 110, range 192-223.
      • /24 prefix length.
    • Class D:
      • First octet begins with 1110, range 224-239.
    • Class E:
      • First octet begins with 1111, range 240-255.
  3. Subnetting Process

    • Step-by-step guide to subnetting to avoid confusion.

Purpose and Need for CIDR

  • Traditional classful addressing leads to wasted IP addresses.
  • Examples of waste:
    • Point-to-point networks using entire /24 networks.
    • Allocating a class B network for 5000 hosts, wasting ~60,000 addresses.
  • IETF introduced CIDR in 1993 to address the inefficiencies.

CIDR and Subnetting

  • CIDR allows smaller subnets by removing rigid class rules:

    • Example: Using /30 or /31 instead of /24 for point-to-point connections.
  • Subnetting Calculations:

    • Formula: 2^number of host bits - 2 (minus network and broadcast addresses).
    • Practice with varying prefix lengths:
      • /30: 2 usable addresses, ideal for point-to-point with 0 wasted.
      • /31: Special case for point-to-point, using both addresses.
      • /32: Used for specific host routes.

Example Scenario

  • Given 192.168.1.0/24 network with 4 subnets needed for 45 hosts each.
  • Calculating subnet sizes:
    • /26 subnet chosen as it supports 62 usable addresses.

Summary

  • CIDR enhances flexibility and efficiency in IP addressing.
  • Subnetting basics covered with emphasis on avoiding waste.
  • Encouragement to practice subnetting with quiz hints.

Additional Resources

  • Flashcards for review.
  • Membership options for supporting the channel.
  • Call to subscribe, like, comment, and share.