What Subnet Mask Would Be Associated With The IPV4 Prefix Of /28?

A /28 IPv4 prefix corresponds to a subnet mask of 255.255.255.240, which supports 16 IP addresses, including 14 usable host addresses. It's ideal for small networks. For more networking tips and exam prep resources, visit Study4Pass your trusted guide to IT certification success.

Tech Professionals

18 April 2025

Cisco

What Subnet Mask Would Be Associated With The IPV4 Prefix Of /28?

Introduction

Understanding subnetting is a fundamental skill for any networking professional, especially for those pursuing certifications like CCNA, CCDA, CCENT, CCNA Security, and CCNA Wireless. One of the most common questions in networking exams is: "What subnet mask would be associated with the IPv4 prefix of /28?"

In this comprehensive guide, we will break down the concept of subnet masks, explain how they relate to CIDR notation (such as /28), and provide practical examples to solidify your understanding. Additionally, we will highlight how Study4Pass can help you master these topics efficiently for your certification exams.

Understanding IPv4 Addressing

Before diving into subnet masks, it's essential to understand IPv4 addressing. An IPv4 address is a 32-bit numerical label assigned to devices in a network. It consists of four octets (8 bits each), separated by dots, such as 192.168.1.1.

IPv4 addresses are divided into two parts:

Network portion (identifies the network)
Host portion (identifies the device within the network)

Since IPv4 addresses are limited (only about 4.3 billion unique addresses), subnetting helps optimize address allocation.

What Is a Subnet Mask?

A subnet mask determines which part of an IP address belongs to the network and which part belongs to the host. Like an IP address, it is a 32-bit number, usually represented in dotted-decimal notation (e.g., 255.255.255.0).

"1" bits represent the network portion.
"0" bits represent the host portion.

For example:

IP: 192.168.1.1
Subnet Mask: 255.255.255.0
- The first 24 bits (three octets) are the network portion.
- The last 8 bits (one octet) are the host portion.

CIDR Notation Explained

CIDR (Classless Inter-Domain Routing) notation is a compact way to represent subnet masks. Instead of writing the full subnet mask (e.g., 255.255.255.0), we use a slash followed by a number (e.g., /24).

The number after the slash (/X) indicates how many bits are used for the network portion.
The remaining bits (32 - X) are used for hosts.

Example:

/24 means 24 network bits → 255.255.255.0
/28 means 28 network bits → What is the subnet mask?

Calculating the Subnet Mask for /28

To find the subnet mask for /28, follow these steps:

Understand the bits:
- A /28 means 28 bits are allocated to the network.
- The remaining 4 bits (32 - 28 = 4) are for hosts.
Convert to binary:
- The first 28 bits are 1s, and the last 4 bits are 0s.
- Binary: 11111111.11111111.11111111.11110000
Convert each octet to decimal:
- First three octets: 255.255.255 (all 1s)
- Fourth octet: 11110000 →
  - 128 + 64 + 32 + 16 = 240
Final subnet mask:
- 255.255.255.240

Conclusion:

The subnet mask associated with the /28 prefix is 255.255.255.240.

Practical Examples of /28 Subnetting

Let’s apply this knowledge with real-world examples.

Example 1: Network Address Calculation

Given IP: 192.168.1.33/28

Subnet Mask: 255.255.255.240

Find the network address:
- Perform a bitwise AND between the IP and subnet mask.
- 192.168.1.33 → 11000000.10101000.00000001.00100001
- 255.255.255.240 → 11111111.11111111.11111111.11110000
- AND Result → 11000000.10101000.00000001.00100000 (192.168.1.32)
- Network Address: 192.168.1.32
Find the broadcast address:
- The last 4 bits (host bits) are set to 1.
- 00100000 (32) → 00101111 (47)
- Broadcast Address: 192.168.1.47
Usable host range:
- 192.168.1.33 to 192.168.1.46

Example 2: Determining Subnet Size

A /28 subnet has:

4 host bits → 2⁴ = 16 total addresses
Usable hosts = 16 - 2 (network & broadcast) = 14

This makes /28 ideal for small networks requiring 14 hosts.

Why Subnetting Matters in Networking?

Subnetting is crucial for:

Efficient IP allocation – Prevents IP wastage.
Improved network performance – Reduces broadcast traffic.
Enhanced security – Isolates network segments.
Simplified management – Organizes networks logically.

For CCNA, CCENT, and other Cisco exams, subnetting is a must-know topic.

Common Subnetting Questions in CCNA Exams

Expect questions like:

"What is the subnet mask for /28?"
"How many usable hosts are in a /28 subnet?"
"What is the broadcast address of 192.168.1.33/28?"

Mastering these ensures exam success.

How Study4Pass Helps You Master Subnetting

Struggling with subnetting? Study4Pass provides:

Structured CCNA/CCENT study guides
Interactive subnetting video tutorials
Practice quizzes with detailed explanations
Real-world subnetting scenarios

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Conclusion

The subnet mask for a /28 IPv4 prefix is 255.255.255.240. Understanding this concept is vital for networking exams like CCNA, CCDA, CCENT, CCNA Security, and CCNA Wireless.

By practicing subnetting and using resources from Study4Pass, you can confidently tackle any subnetting question in your certification exams.

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