Understanding Subnet Masks

Introduction

• Subnet Mask Topic: Explanation of what a subnet mask is and its significance in networking.

Basics of IP Addresses

• IP Address: Identifier for a computer or device on a network.
• IPv4 Address: 32-bit numeric address divided into four octets (e.g., 192.168.1.1).
  • Each octet ranges from 0 to 255.
• Parts of an IP Address:
  • Network Address/ID: Unique identifier for a network.
  • Host Address/ID: Unique identifier for hosts within a network.

Subnet Masks Explained

• Subnet Mask: Number similar to an IP address that distinguishes the network and host portions of the IP address.
• Binary Format: Computers read IP addresses and subnet masks as binary numbers (1s and 0s).
• 8-bit Octet Chart: Helps convert IP addresses and subnet masks to binary.
  • Each bit has a value doubling from right to left (1, 2, 4, 8, etc.).

Converting IP Address to Binary

1. 192 in Binary: 11000000
2. 168 in Binary: 10101000
3. 1 in Binary: 00000001
4. 0 in Binary: 00000000

Converting Subnet Mask to Binary

• 255 in Binary: 11111111
• 224 in Binary (explained with bits): 11100000
• Example Subnets:
  1. 255.255.0.0: Network portion in the first two octets.
  2. 255.255.255.0: Network portion in the first three octets.
  3. 255.255.255.224: Network portion includes part of the third octet.

Importance of Network and Host Parts

• Purpose: To manage and divide large networks into smaller networks (subnets).
• Broadcasts: How computers locate each other in a network, affected by network size.
• Routers: Used to separate networks and control broadcast traffic, enhancing network performance.
• Subnetting: Process of dividing a large network into smaller subnets using subnet masks.

Example of Subnetting

• Small Business Scenario:
  • Initial Network: 12 computers on a single network.
  • Goal: Separate into 3 smaller networks.
  • Method: Change subnet mask to divide the network using bits.

Subnet Masks and Number of Hosts

• Borrowing Bits: Changes the default subnet mask to create more networks.
  1. Borrowing 1 bit: 2 subnets, 126 hosts each.
  2. Borrowing 2 bits: 4 subnets, 62 hosts each.
  3. Borrowing 3 bits: 8 subnets, 30 hosts each.
  4. ...up to 7 bits resulting in unusable hosts.

Subnet Classes and CIDR Notation

• IP Address Classes (A, B, C) with corresponding default subnet masks.
  • Class A: Large organizations (up to 16 million hosts).
  • Class B: Medium to large organizations (up to 65,000 hosts).
  • Class C: Small organizations, homes (up to 254 hosts).
• CIDR Notation: Classless Inter-Domain Routing
  • E.g., /24 for a subnet mask with 24 bits as 1s.
  • Other examples: /25, /26, /8.

Conclusion

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