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The Complete Subnet Cheat Sheet: Master Network Administration

The Complete Subnet Cheat Sheet: Master Network Administration

Introduction

Network subnetting is a fundamental skill for anyone managing dedicated servers, VPS hosting, or cloud hosting infrastructure. Whether you’re setting up a new hosting environment or troubleshooting network connectivity issues, understanding subnets is crucial for optimal server performance and security.

What is Subnetting?

Subnetting is the practice of dividing a network into smaller, more manageable sub-networks (subnets). This technique is essential for hosting providers and system administrators who need to efficiently allocate IP addresses across multiple servers, implement security boundaries, and optimize network performance for shared hosting and dedicated hosting environments.

Why Subnetting Matters for Web Hosting

In modern hosting infrastructure, subnetting provides several critical benefits:

 

  • Enhanced Security: Isolate different hosting clients and services
  • Improved Performance: Reduce broadcast traffic across server networks
  • Efficient IP Management: Maximize the use of available IP addresses
  • Network Organization: Structure hosting environments logically
  • Scalability: Easily expand hosting capacity as needed

CIDR Subnet Reference Table

CIDRSubnet MaskWildcard Mask# of IP Addresses# of Usable IP Addresses
/32255.255.255.2550.0.0.011
/31255.255.255.2540.0.0.122*
/30255.255.255.2520.0.0.342
/29255.255.255.2480.0.0.786
/28255.255.255.2400.0.0.151614
/27255.255.255.2240.0.0.313230
/26255.255.255.1920.0.0.636462
/25255.255.255.1280.0.0.127128126
/24255.255.255.00.0.0.255256254
/23255.255.254.00.0.1.255512510
/22255.255.252.00.0.3.2551,0241,022
/21255.255.248.00.0.7.2552,0482,046
/20255.255.240.00.0.15.2554,0964,094
/19255.255.224.00.0.31.2558,1928,190
/18255.255.192.00.0.63.25516,38416,382
/17255.255.128.00.0.127.25532,76832,766
/16255.255.0.00.0.255.25565,53665,534
/15255.254.0.00.1.255.255131,072131,070
/14255.252.0.00.3.255.255262,144262,142
/13255.248.0.00.7.255.255524,288524,286
/12255.240.0.00.15.255.2551,048,5761,048,574
/11255.224.0.00.31.255.2552,097,1522,097,150
/10255.192.0.00.63.255.2554,194,3044,194,302
/9255.128.0.00.127.255.2558,388,6088,388,606
/8255.0.0.00.255.255.25516,777,21616,777,214
/7254.0.0.01.255.255.25533,554,43233,554,430
/6252.0.0.03.255.255.25567,108,86467,108,862
/5248.0.0.07.255.255.255134,217,728134,217,726
/4240.0.0.015.255.255.255268,435,456268,435,454
/3224.0.0.031.255.255.255536,870,912536,870,910
/2192.0.0.063.255.255.2551,073,741,8241,073,741,822
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,646
/00.0.0.0255.255.255.2554,294,967,2964,294,967,294

* /31 networks are a special case typically used for point-to-point links where only two addresses are needed.

Decimal to Binary Conversion Table for Subnet Masks and Wildcards

Understanding the binary representation of subnet masks is essential for hosting administrators. Here’s a comprehensive conversion table:

Subnet Mask Reference
DecimalBinarySubnet Mask UsageWildcard MaskBinary (Wildcard)
000000000No network bits25511111111
128100000001 network bit12701111111
192110000002 network bits6300111111
224111000003 network bits3100011111
240111100004 network bits1500001111
248111110005 network bits700000111
252111111006 network bits300000011
254111111107 network bits100000001
255111111118 network bits000000000

What Does CIDR Mean and What is CIDR Notation?

CIDR (Classless Inter-Domain Routing) revolutionized how hosting providers manage IP addresses by eliminating the rigid Class A, B, and C boundaries. CIDR allows for more efficient IP allocation and is essential for modern hosting infrastructure.

CIDR Notation Explained:

CIDR notation uses a forward slash followed by a number to indicate the network portion of an IP address:

Format: IP Address/Prefix Length

Example: 192.168.1.0/24

 

  • IP Address: 192.168.1.0
  • Prefix Length: /24 (first 24 bits represent the network)
  • Host Bits: 32 – 24 = 8 bits (256 possible addresses)