IP Subnet Cheat Sheet

Basic Concepts link

IP Address Classes link

IP addresses are divided into different classes based on their leading bits. Here’s a quick overview:

• Class A: 1.0.0.0 to 126.0.0.0

  • Default Subnet Mask: 255.0.0.0 (/8)
  • Number of Networks: 128 (2^7)
  • Hosts per Network: 16,777,214
  
  

• Class B: 128.0.0.0 to 191.255.0.0

  • Default Subnet Mask: 255.255.0.0 (/16)
  • Number of Networks: 16,384 (2^14)
  • Hosts per Network: 65,534
  
  

• Class C: 192.0.0.0 to 223.255.255.0

  • Default Subnet Mask: 255.255.255.0 (/24)
  • Number of Networks: 2,097,152 (2^21)
  • Hosts per Network: 254

Private IP Address Ranges link

Private IP addresses are used within a network and are not routable on the internet. Here are the ranges:

• Class A: 10.0.0.0 to 10.255.255.255
• Class B: 172.16.0.0 to 172.31.255.255
• Class C: 192.168.0.0 to 192.168.255.255

Subnet Masks and CIDR Notation link

Subnet masks define the network and host portions of an IP address. CIDR (Classless Inter-Domain Routing) notation specifies the subnet mask in a compact form.

Quick Reference for Common Subnets link

Class A Subnetting link

Class B Subnetting link

Class C Subnetting link

Special IP Address Ranges link

IP address ranges have specific purposes, from local communication to testing and future use. Here’s a detailed look at these special IP address ranges, presented in a more visual and structured format.

Reserved and Private Ranges link

Documentation and Testing link

Specialized Purposes link

Visual Explanation and Practical Examples link

APIPA (Automatic Private IP Addressing) link

• Range: 169.254.0.0/16
• Usage: When a device can’t obtain an IP from DHCP, it auto-assigns an address within this range.
• Example: A device might use 169.254.45.1 to communicate locally.

+---------------------+
| Device A            |
| IP: 169.254.45.1    |
+---------------------+
         |
         | (Link-local communication)
         |
+---------------------+
| Device B            |
| IP: 169.254.45.2    |
+---------------------+

Loopback Address link

• Range: 127.0.0.0/8
• Usage: Test network software without external network. Commonly used address: 127.0.0.1.
• Example: Web developers testing a web server on their local machine.

+---------------------------+
| Local Machine             |
|                           |
| Test Web Server:          |
| http://127.0.0.1          |
+---------------------------+

Private Network Addresses link

+----------------------------------------------+
| Home Router                                  |
|                                              |
| +-------------------+     +----------------+ |
| | Device A          |     | Device B       | |
| | IP: 192.168.1.2   |     | IP: 192.168.1.3| |
| +-------------------+     +----------------+ |
|                                              |
| Private Network: 192.168.1.0/24              |
+----------------------------------------------+

Practical Usage of Special IP Ranges link

Broadcast Address (255.255.255.255) link

• Usage: Send a message to all devices in the local network segment.
• Example: A DHCP request might be broadcast to 255.255.255.255.

Multicast Address (224.0.0.0/4) link

• Usage: Stream data to multiple devices simultaneously.
• Example: Video conferencing tools often use multicast to distribute video streams.

Common Calculations link

Determining Subnet Range link

1. Identify the subnet mask.
2. Calculate the block size: 256 - the value in the subnet mask's relevant octet.
3. List subnet ranges using the block size.

For example link

For 192.168.1.0/26:

1. Subnet Mask: 255.255.255.192
2. Block Size: 256 - 192 = 64
3. Subnets:
   • 192.168.1.0 - 192.168.1.63
   • 192.168.1.64 - 192.168.1.127
   • 192.168.1.128 - 192.168.1.191
   • 192.168.1.192 - 192.168.1.255

Calculating Usable Hosts link

• Formula: 2^n - 2
  • n = number of host bits.
• Example for /26:
  • Host Bits: 32 - 26 = 6
  • Usable Hosts: 2^6 - 2 = 62

Binary to Decimal Conversion link

Understanding binary to decimal conversion is key in subnetting:

• Powers of 2: 2^0 = 1, 2^1 = 2, 2^2 = 4, …, 2^8 = 256
• Example: Binary 11000000 equals decimal 192.

Subnetting Practice Exercises link

1. Determine the number of subnets and hosts per subnet for a given CIDR.
2. Practice converting binary to decimal and vice versa.
3. Calculate subnet ranges and broadcast addresses.

Quick Tips link

• Memorize Common Subnet Masks and CIDR Notations.
• Use Incremental Values for easy subnet calculation.
• Plan for Future Growth: Allocate larger subnets than currently needed.
• Document Your Subnetting Scheme: Keep a record of your IP address allocations and network design.
• Practice, Practice, Practice: Regular practice with different scenarios will improve your subnetting skills.

Conclusion link

This cheat sheet serves as a quick reference to essential subnetting information, equipping you with the knowledge needed to efficiently design and manage IP networks. By familiarizing yourself with these special IP address ranges, you can ensure proper allocation of IP addresses and avoid conflicts.

Understanding these ranges allows network administrators to:

• Design Efficient Networks: Plan and implement network segments that are both scalable and organized.
• Avoid IP Conflicts: Use reserved and private IP ranges correctly to prevent address overlap and connectivity issues.
• Troubleshoot Effectively: Quickly identify and resolve network issues by recognizing the significance of different IP ranges.
• Plan for the Future: Allocate IP addresses with foresight, considering potential network growth and changes.

With this cheat sheet at your disposal, you’ll be well-prepared to handle the complexities of subnetting and IP address management. Happy subnetting!