CCNA | Subnetting (Part 1) | Day 13 |

Introduction to Subnetting

• Welcome to Jeremy's IT Lab, a free CCNA course.

• Importance of subnetting in networking.

• Aim to simplify the concept of subnetting.

• Video segmented into two or three parts for better understanding.

CIDR (Classless Interdomain Routing)

• CIDR stands for Classless Inter-Domain Routing.

• Developed to increase flexibility in IPv4 addressing.

• Moves away from rigid Class A, B, C addressing.

Overview of IPv4 Address Classes

• Five classes of IPv4 addresses: A, B, C, D, E.

Class A

• Begins with 0 in the first octet.

• Decimal range: 0 to 127.

• IP Address Range: 0.0.0.0 to 127.255.255.255.

• Prefix Length: /8 (first octet for network, 3 for hosts).

• Large usable address space: ~16,777,216 addresses.

Class B

• Begins with 10 in the first octet.

• Decimal range: 128 to 191.

• IP Address Range: 128.0.0.0 to 191.255.255.255.

• Prefix Length: /16 (first two octets for network, 2 for hosts).

• Usable addresses: ~65,536.

Class C

• Begins with 110 in the first three bits.

• Decimal range: 192 to 223.

• IP Address Range: 192.0.0.0 to 223.255.255.255.

• Prefix Length: /24 (first three octets for network, last one for hosts).

• Usable addresses: 256.

Class D

• Begins with 1110 (used for multicast).

• Decimal range: 224 to 239.

Class E

• Begins with 1111 (reserved for future use).

• Decimal range: 240 to 255.

Issues with Classful Addressing

• Classful addressing can lead to wasted IP addresses.

• Example of point-to-point connection leads to underutilization.

• Companies assigned network ranges based on size (Class A for large, Class C for small).

Transition to CIDR

• Introduced by the IETF in 1993.

• Removes strict class rules, allows for variable-length subnet masking.

• Improves efficiency in allocation.

Example of Subnetting

• Re-evaluating a point-to-point network using CIDR.

• Addresses can be assigned in smaller blocks according to requirements.

Calculating Usable Addresses

• Formula for usable addresses: 2^n - 2, where n = number of host bits.

CIDR Notation and Subnet Masks

• CIDR uses a slash (/) notation to denote prefix length.

• Example: /24 corresponds to 255.255.255.0.

Practice Calculation Tasks

• Example with 203.0.113.0 network to illustrate usable addresses for different prefix lengths:

  • /24: 254 usable addresses.

  • /25: 126 usable addresses.

  • /26: 62 usable addresses.

  • /27: 30 usable addresses.

  • /28: 14 usable addresses.

  • /29: 6 usable addresses.

  • /30: 2 usable addresses (4 total).

  • /31: 0 usable addresses, but usable for point-to-point links.

  • /32: Not really usable for general networking but can specify one host.

Characteristics of 31 and 32 Networks

• Using /31 allows addressing two routers directly.

• /32 is generally used in static configurations for specific hosts.

Summary of Key Points

• CIDR provides flexibility over traditional classful addressing.

• Understanding how to subnet efficiently saves IP addresses and optimizes network usage.

Upcoming Content

• Next video will cover practice problems and provide practical exercises on subnetting.

• A final task mentioned to find subnets for a network with specific requirements.

Calls to Action

• Encourage viewers to like, comment, and subscribe to support the series.

• Offer links for supplementary materials (flashcards).

• Membership options available for further support.