IPv4 Addressing and Subnetting

This article provides a detailed description of IPv4 address ranges, classes (A, B, and C), and subnetting, including examples of available addresses for various subnet masks (/22 to /32). To gather this information, the following research steps were conducted:

1. Information was collected on IP address classes (A, B, C) and their respective address ranges.

2. The concept of subnet masks and their use in dividing networks into smaller subnets was explored.

3. The concepts of network identifier, broadcast address, and usable IP addresses within a subnet were investigated.

4. Based on the gathered information, a table was created to illustrate the network identifier, broadcast address, usable IP addresses, and examples of available addresses (within the range of 1-1024) for each IP address class (A, B, C) and subnet mask (/22 to /32).

5. Reserved addresses (network identifier and broadcast address) were highlighted for each subnet mask.

An IP address is a unique numerical identifier assigned to every device connected to a computer network that uses the Internet Protocol for communication. Similar to a street address that identifies a specific building, an IP address allows devices to send and receive data over a network1. IPv4 addresses are 32-bit numbers, often represented in dotted decimal notation (e.g., 192.168.1.1)2.

IP Address Classes

IPv4 addresses are categorized into five classes: A, B, C, D, and E. Classes A, B, and C provide unicast addresses for networks of three different network sizes. Class D is reserved for multicast, which involves sending data to a group of devices simultaneously. Class E is reserved for experimental purposes.

Historically, IP address classes were designed to accommodate networks of different sizes. Class A, with a range of 0-127 in the first byte, was intended for very large companies. Class B (128-191) was designed for medium-sized companies, and Class C (192-223) was for small companies3. This method of assigning IP addresses is known as "classful" addressing. However, classful addressing proved to be inefficient due to the rigid structure and allocation of address blocks4. This led to the development of "classless" addressing, also known as Classless Inter-Domain Routing (CIDR), which allows for more flexible allocation of IP addresses.

Each class has a different address range and a default subnet mask, which determines how many bits of the IP address are used to identify the network and how many are used to identify the host within that network5.

Note: The address ranges 0.0.0.0/8 and 127.0.0.0/8 in Class A, 128.0.0.0/16 and 191.255.0.0/16 in Class B, and 192.0.0.0/24 and 223.255.255.0/24 in Class C were initially reserved but are now mostly available for assignment.

Special IP Addresses

Within the IP address classes, certain addresses are reserved for specific purposes:

• Loopback Address (127.0.0.1): This address is used to test network connectivity on the local machine. Any data sent to this address is looped back to the sending device6.

• Private IP Addresses: These addresses are used within private networks and are not routable on the public internet. The reserved ranges for private IP addresses are:

• 10.0.0.0/8

• 172.16.0.0/12

• 192.168.0.0/16 7

Class E Addresses

Class E addresses, with the first four network address bits set to 1 (240.0.0.0 to 255.255.255.255), are reserved. However, their usage was never fully defined. As a result, most network implementations discard these addresses as illegal or undefined6.

Subnet Masks and Subnetting

A subnet mask is a 32-bit number that helps divide a network into smaller, more manageable segments called subnets. It works by "masking" a portion of the IP address to identify the network address, while the remaining bits identify the host within that subnet8.

A subnet mask is expressed in the same format as an IP address, such as 255.255.255.0. In binary notation, the subnet mask consists of a series of 1s followed by 0s. The 1s represent the network portion of the address, and the 0s represent the host portion9. The number of zeros in the subnet mask's binary representation determines the number of host addresses in the subnet9.

For example, the subnet mask 255.255.255.0 in binary is 11111111.11111111.11111111.00000000. This mask has eight zeros, which means it can accommodate 2⁸ (256) addresses. However, two of these addresses are reserved (network identifier and broadcast address), leaving 254 usable host addresses.

Wildcard Masks

A wildcard mask is the inverse of a subnet mask. It is also a 32-bit number, but the bits that are 1s in the subnet mask are 0s in the wildcard mask, and vice versa. Wildcard masks are often used in access control lists (ACLs) to define a range of IP addresses that are permitted or denied access8.

Benefits of Subnetting

Subnetting offers several benefits:

• Efficient IP Address Management: Subnetting allows for better utilization of IP addresses by dividing large address spaces into smaller segments. This prevents wastage of IP addresses and helps organizations with multiple departments or locations allocate addresses logically10.

• Improved Network Performance: By creating smaller broadcast domains, subnetting reduces network congestion and improves overall performance. Data packets don't have to travel as far, leading to faster communication8.

• Enhanced Security: Subnetting allows for the isolation of different parts of a network, improving security by limiting the impact of broadcasts and potential security breaches11.

Subnetting and Number of Hosts

A key insight in subnetting is the relationship between the subnet mask and the number of usable hosts in a subnet. Larger subnet masks (e.g., /28) result in fewer usable hosts per subnet, while smaller subnet masks (e.g., /22) provide more usable hosts7. This creates a trade-off between the number of subnets and the number of hosts per subnet. Increasing the number of subnets reduces the number of usable hosts per subnet, and vice versa.

For example, a /24 subnet allows for 254 usable hosts, while a /25 subnet allows for only 126 usable hosts. However, subnetting with a /25 mask creates two subnets instead of one.

Careful Planning in Subnetting

Careful planning and accurate calculations are essential when subnetting a network. Proper network design and the use of subnet calculators can help avoid errors and ensure efficient IP address allocation8. Mistakes in subnetting can lead to overlapping subnets, wasted IP addresses, and network performance issues.

Network Identifier and Broadcast Address

Within each subnet, two IP addresses are reserved:

• Network Identifier: The first address in the subnet range is the network identifier. It represents the subnet itself and is used for routing purposes3.

• Broadcast Address: The last address in the subnet range is the broadcast address. It is used to send data to all devices within that subnet simultaneously13.

These two addresses cannot be assigned to individual hosts12.

Determining Network and Broadcast Addresses

To determine the network and broadcast addresses of a subnet, you need the IP address of a device within the subnet and the subnet mask4. Here's a step-by-step example:

1. Convert the IP address and subnet mask to binary form. For example, let's use the IP address 192.168.1.100 and the subnet mask 255.255.255.192 (/26).

2. IP address in binary: 11000000.10101000.00000001.01100100

3. Subnet mask in binary: 11111111.11111111.11111111.11000000

4. Perform a bitwise AND operation between the binary IP address and the binary subnet mask. This isolates the network address.11000000.10101000.00000001.01100100 (IP address)11111111.11111111.11111111.11000000 (Subnet mask)----------------------------------11000000.10101000.00000001.01000000 (Network address)

5. Convert the binary network address back to decimal form. This gives us 192.168.1.64.

6. To find the broadcast address, change all the host bits (the 0s in the subnet mask) to 1s in the network address.11000000.10101000.00000001.01000000 (Network address)11000000.10101000.00000001.01111111 (Broadcast address)

7. Convert the binary broadcast address back to decimal form. This gives us 192.168.1.127.

Therefore, the network identifier is 192.168.1.64, and the broadcast address is 192.168.1.127.

Direct and Limited Broadcast Addresses

In addition to the regular broadcast address within a subnet, there are two special types of broadcast addresses:

• Direct broadcast address: This address is used to send information to all hosts on a specific network. It is formed by setting all the host bits in the IP address to 1s. For example, the direct broadcast address for the subnet 192.168.1.0/24 is 192.168.1.2553.

• Limited broadcast address: This address (255.255.255.255) is used to send information to all hosts on the same network as the sending host3.

Broadcast Addresses in Network Discovery

Broadcast addresses play a crucial role in network discovery protocols, such as the Address Resolution Protocol (ARP). ARP uses broadcast messages to map IP addresses to MAC addresses within a local network. When a device wants to communicate with another device on the same network, it sends an ARP request with the target device's IP address to the broadcast address. All devices on the network receive the request, but only the device with the matching IP address responds with its MAC address14.

Usable IP Addresses

The IP addresses between the network identifier and the broadcast address are the usable IP addresses that can be assigned to devices within the subnet. The number of usable IP addresses depends on the subnet mask12.

For example, a /24 subnet mask has 256 total addresses, but only 254 are usable because the first and last addresses are reserved for the network identifier and broadcast address, respectively12.

Examples of Available Addresses

The following table shows examples of available addresses within the range of 1-1024 for different subnet masks, along with the reserved network identifier and broadcast address:

Note: /31 and /32 subnets are special cases. /31 subnets are used for point-to-point links that don't require a local broadcast, and /32 subnets are used for loopback addresses where there is only one device in the subnet12.

Network Address Translation (NAT)

Network Address Translation (NAT) is a technique used to allow devices with private IP addresses to access the internet. NAT works by translating the private IP addresses of devices within a local network to a public IP address before the traffic is sent to the internet7. This allows multiple devices within a private network to share a single public IP address.

NAT is a crucial technology for conserving public IPv4 addresses, as it allows organizations to use private IP addresses internally while still providing internet access to their devices.

IP Address Management (IPAM)

IP Address Management (IPAM) tools are essential for managing IP addresses and subnet allocations within a network. These tools provide comprehensive visibility into IP address usage, allowing administrators to monitor available addresses, plan for future needs, and avoid conflicts10.

IPAM tools can automate many IP address management tasks, such as assigning IP addresses to devices, tracking address usage, and generating reports. This helps network administrators ensure efficient and organized IP address allocation.

Common Subnetting Mistakes

While subnetting offers many benefits, it's important to avoid common mistakes that can lead to network problems:

• Inaccurate calculation of subnet sizes: Incorrectly calculating the number of hosts or subnets can result in insufficient addresses or wasted IP space.

• Extensive range of subnets: Creating subnets with too many devices can increase broadcast traffic and impact network performance.

• Scattered subnets: Poorly planned subnetting can lead to inefficient routing and increased network complexity8.

To avoid these mistakes, careful planning, accurate calculations, and the use of subnetting tools are crucial.

Summary

IP addressing and subnetting are fundamental concepts in computer networking. Understanding IP address classes, subnet masks, and the principles of subnetting is crucial for network administrators and anyone working with computer networks. By properly configuring IP addresses and subnet masks, you can ensure efficient network communication, optimize resource utilization, and improve network security.

This article provided a comprehensive overview of IPv4 addressing and subnetting, covering various aspects such as IP address classes, subnet masks, network identifiers, broadcast addresses, usable IP addresses, and common subnetting mistakes. By understanding these concepts and applying them correctly, you can effectively manage your network and ensure optimal performance and security.

Works cited

1. What is IP Addressing and Subnetting? IP Addressing Guide - Civo.com, accessed on February 16, 2025, https://www.civo.com/learn/ip-addressing

2. Classful network - Wikipedia, accessed on February 16, 2025, https://en.wikipedia.org/wiki/Classful_network

3. Finding the Subnet ID | NetworkAcademy.io, accessed on February 16, 2025, https://www.networkacademy.io/ccna/ip-subnetting/finding-the-subnet-id

4. Determining Network and Broadcast Address Using IP Address and Subnet Mask | Baeldung on Computer Science, accessed on February 16, 2025, https://www.baeldung.com/cs/ip-address-subnet-mask

5. Understand TCP/IP addressing and subnetting basics - Microsoft Learn, accessed on February 16, 2025, https://learn.microsoft.com/en-us/troubleshoot/windows-client/networking/tcpip-addressing-and-subnetting

6. IP address - Definition and Details - Paessler, accessed on February 16, 2025, https://www.paessler.com/it-explained/ip-address

7. Understanding Address spaces and subnetting in IPv4 [Tutorial] - Packt, accessed on February 16, 2025, https://www.packtpub.com/en-us/learning/how-to-tutorials/understanding-address-spaces-and-subnetting-in-ipv4-tutorial

8. What Is a Subnet Mask? 2024 Updated Guide - IPXO, accessed on February 16, 2025, https://www.ipxo.com/blog/what-is-subnet-mask/

9. Mastering Subnet Masks for Efficient Network Management | Lenovo USOutlet, accessed on February 16, 2025, https://www.lenovo.com/us/outletus/en/glossary/subnet-mask/

10. Subnet Explained: What is it & how does it work - UptimeRobot Knowledge Hub, accessed on February 16, 2025, https://uptimerobot.com/knowledge-hub/devops/subnet-explained/

11. Understanding Subnet Masks: A Technical Overview | Orhan Ergun, accessed on February 16, 2025, https://orhanergun.net/understanding-subnet-masks-a-technical-overview

12. Subnetting: What It Is and How It Works | Auvik, accessed on February 16, 2025, https://www.auvik.com/franklyit/blog/subnetting-primer/

13. Network Address Broadcast Address and IP Address Explained, accessed on February 16, 2025, https://www.computernetworkingnotes.com/networking-tutorials/network-address-broadcast-address-and-ip-address-explained.html

14. What Is a Broadcast IP Address? - WhatIsMyIP.com®, accessed on February 16, 2025, https://www.whatismyip.com/broadcast-address/

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In the spirit of variety, I have added some examples of IPv4 address and subnetting due to a fellow student leaving a class while an instructor was teaching subnetting. The student had learned subnetting a different way than the instructor explained the subject, so they left the room for an hour so he would get confused.

It's tricky to give specific examples of available addresses in the 1-1024 range because those addresses are part of the public IPv4 space, and their availability changes constantly. Think of it like phone numbers – some are in use, some aren't, and you can't just pick one and assume it's free.

However, I can break down the structure and reserved portions within that range to illustrate how it works:

Understanding the Structure

• Class A: The 1-1024 range falls mostly within Class A. These addresses are designed for large networks.

• Network Portion: The first octet (the first number) largely defines the network. In Class A, the first octet is between 1 and 126.

• Host Portion: The remaining octets identify specific devices (hosts) within that network.

Example Breakdown (Simplified)

Let's imagine a tiny slice of the 1.0.0.0/8 network (a Class A network):

• Network: 1.0.0.0

• Usable Range: 1.0.0.1 to 1.255.255.254 (a huge number of addresses!)

• Broadcast: 1.255.255.255 (this address is reserved; sending data to it reaches ALL devices on that network)

Why "Available" is Tricky

• IANA Allocation: The Internet Assigned Numbers Authority (IANA) distributes blocks of these addresses to regional internet registries (RIRs).

• RIR Distribution: RIRs then allocate smaller blocks to internet service providers (ISPs), organizations, etc.

• Dynamic Use: These addresses are assigned and reassigned as needed. What's "available" today might be in use tomorrow.

Reserved Addresses

Within any IPv4 network, certain addresses are reserved:

• Network Identifier: The very first address in a block (e.g., 1.0.0.0 in our example) is the network identifier itself. It's not assigned to a specific device.

• Broadcast Address: The very last address (e.g., 1.255.255.255) is the broadcast address.

Important Notes

• Subnetting: Networks are often divided into smaller subnets. This changes the available ranges and reserved addresses within each subnet.

• Private Addresses: Remember, there are also private IP ranges (10.x.x.x, 192.168.x.x, etc.) that are for use within local networks and don't need to be publicly registered.

If you need a specific IP address:

• Home/Small Business: Your ISP will assign you one.

• Larger Organization: You'd likely get a block from your RIR or through a broker.

It's a complex system, but hopefully this gives you a clearer picture of how the 1-1024 range fits into it!

Details description of ip4 address range with examples of available address 1-1024 /22,/23,/24,/25,/26,/27,/28,/29,/30/31,/32,and highlight the reserved address for each identifier and broadcast

Okay, let's dive into the IPv4 address range 1-1024 with those subnet masks, keeping in mind that these are public addresses and their actual availability is dynamic.

Understanding Subnet Masks

A subnet mask helps define how much of an IP address is used for the network portion and how much is for the host portion. A smaller subnet mask (like /22) means more addresses for hosts but fewer networks. A larger subnet mask (like /30) means the opposite.

Breaking Down the Ranges

Here's how the 1-1024 range can be divided with the given subnet masks, along with examples and reserved addresses:

• /22 (1024 addresses)

  • Example Network: 1.0.0.0/22

  • Usable Range: 1.0.0.1 to 1.0.3.254

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.3.255

  • Explanation: This gives you one large block of 1024 addresses.

• /23 (512 addresses)

  • Example Network: 1.0.0.0/23

  • Usable Range: 1.0.0.1 to 1.0.1.254

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.1.255

  • Explanation: This splits the /22 into two smaller blocks of 512.

• /24 (256 addresses)

  • Example Network: 1.0.0.0/24

  • Usable Range: 1.0.0.1 to 1.0.0.254

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.255

  • Explanation: This is a very common size, often used for small networks.

• /25 (128 addresses)

  • Example Network: 1.0.0.0/25

  • Usable Range: 1.0.0.1 to 1.0.0.126

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.127

  • Explanation: This further divides the /24 in half.

• /26 (64 addresses)

  • Example Network: 1.0.0.0/26

  • Usable Range: 1.0.0.1 to 1.0.0.62

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.63

  • Explanation: Useful for even smaller subnets.

• /27 (32 addresses)

  • Example Network: 1.0.0.0/27

  • Usable Range: 1.0.0.1 to 1.0.0.30

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.31

  • Explanation: Getting into very small network sizes.

• /28 (16 addresses)

  • Example Network: 1.0.0.0/28

  • Usable Range: 1.0.0.1 to 1.0.0.14

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.15

  • Explanation: Often used for point-to-point links or very small isolated networks.

• /29 (8 addresses)

  • Example Network: 1.0.0.0/29

  • Usable Range: 1.0.0.1 to 1.0.0.6

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.7

  • Explanation: Tiny networks, sometimes for specific device connections.

• /30 (4 addresses)

  • Example Network: 1.0.0.0/30

  • Usable Range: 1.0.0.1 to 1.0.0.2

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.3

  • Explanation: Almost always used for direct links between two devices.

• /31 (2 addresses)

  • Example Network: 1.0.0.0/31

  • Usable Range: 1.0.0.1 to 1.0.0.1

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.1

  • Explanation: This is a special case. With a /31 mask, there is no distinct broadcast address. It's used for point-to-point links, and both addresses are assigned to the two devices connected.

• /32 (1 address)

  • Example Network: 1.0.0.0/32

  • Usable Range: 1.0.0.0 to 1.0.0.0

  • Network ID: 1.0.0.0

  • Broadcast: 1.0.0.0

  • Explanation: This is a single IP address, not a network. It's used to identify a specific device.

Key Points

• Availability: Remember that these are just examples. The actual availability of these addresses within the 1-1024 range depends on IANA and RIR allocations.

• Network/Broadcast: The network ID and broadcast address are always reserved within each subnet.

• Subnetting: Subnetting allows you to efficiently use IP addresses by dividing larger blocks into smaller ones as needed.

IPv4 addresses are 32-bit numerical labels used to identify devices on a network. They are typically written in dotted-decimal format, such as 192.168.1.1. Each part of the address is an 8-bit number ranging from 0 to 255.

Here's a detailed example with a range of available addresses from 1.0.0.1 to 1.0.3.255 (which covers 1024 addresses):

Breakdown of the Address Range

1. Network Address: The first address in the range, 1.0.0.0, is reserved as the network identifier. It is not assigned to any individual device.

2. Available Addresses: Addresses from 1.0.0.1 to 1.0.3.254 are available for assignment to devices.

3. Broadcast Address: The last address in the range, 1.0.3.255, is reserved as the broadcast address, used for sending data to all devices on the network.

Example Addresses

Here is a more detailed breakdown of the address range, with highlighted reserved addresses:

So, to summarize:

• Network Addresses: 1.0.0.0, 1.0.1.0, 1.0.2.0, 1.0.3.0

• Available Addresses: 1.0.0.1 to 1.0.3.254

• Broadcast Addresses: 1.0.0.255, 1.0.1.255, 1.0.2.255, 1.0.3.255

These reserved addresses ensure that the network and broadcast functions can operate correctly without interference. If you have any further questions or need more detailed explanations, feel free to ask!

Alright, let’s delve into the details of IPv4 address ranges for Class A, B, and C networks, along with examples for various subnets from /22 to /32. We'll highlight the network identifier and broadcast addresses for each.

Class A IP Address Range

• Range: 1.0.0.0 to 126.255.255.255

• Default Subnet Mask: 255.0.0.0

• Network Bits: 8

• Host Bits: 24

Class B IP Address Range

• Range: 128.0.0.0 to 191.255.255.255

• Default Subnet Mask: 255.255.0.0

• Network Bits: 16

• Host Bits: 16

Class C IP Address Range

• Range: 192.0.0.0 to 223.255.255.255

• Default Subnet Mask: 255.255.255.0

• Network Bits: 24

• Host Bits: 8

Now, let’s break down the address ranges and subnets for each class:

Class A Examples

/22 Subnet (Subnet Mask: 255.255.252.0)

• Range: 1.0.0.0 to 1.0.3.255

• Network Address: 1.0.0.0

• Broadcast Address: 1.0.3.255

• Available Addresses: 1.0.0.1 to 1.0.3.254

/23 Subnet (Subnet Mask: 255.255.254.0)

• Range: 1.0.0.0 to 1.0.1.255

• Network Address: 1.0.0.0

• Broadcast Address: 1.0.1.255

• Available Addresses: 1.0.0.1 to 1.0.1.254

/24 Subnet (Subnet Mask: 255.255.255.0)

• Range: 1.0.0.0 to 1.0.0.255

• Network Address: 1.0.0.0

• Broadcast Address: 1.0.0.255

• Available Addresses: 1.0.0.1 to 1.0.0.254

Class B Examples

/22 Subnet (Subnet Mask: 255.255.252.0)

• Range: 128.0.0.0 to 128.0.3.255

• Network Address: 128.0.0.0

• Broadcast Address: 128.0.3.255

• Available Addresses: 128.0.0.1 to 128.0.3.254

/23 Subnet (Subnet Mask: 255.255.254.0)

• Range: 128.0.0.0 to 128.0.1.255

• Network Address: 128.0.0.0

• Broadcast Address: 128.0.1.255

• Available Addresses: 128.0.0.1 to 128.0.1.254

/24 Subnet (Subnet Mask: 255.255.255.0)

• Range: 128.0.0.0 to 128.0.0.255

• Network Address: 128.0.0.0

• Broadcast Address: 128.0.0.255

• Available Addresses: 128.0.0.1 to 128.0.0.254

Class C Examples

/22 Subnet (Subnet Mask: 255.255.252.0)

• Range: 192.0.0.0 to 192.0.3.255

• Network Address: 192.0.0.0

• Broadcast Address: 192.0.3.255

• Available Addresses: 192.0.0.1 to 192.0.3.254

/23 Subnet (Subnet Mask: 255.255.254.0)

• Range: 192.0.0.0 to 192.0.1.255

• Network Address: 192.0.0.0

• Broadcast Address: 192.0.1.255

• Available Addresses: 192.0.0.1 to 192.0.1.254

/24 Subnet (Subnet Mask: 255.255.255.0)

• Range: 192.0.0.0 to 192.0.0.255

• Network Address: 192.0.0.0

• Broadcast Address: 192.0.0.255

• Available Addresses: 192.0.0.1 to 192.0.0.254

Summary Table

These examples illustrate how IPv4 addresses are divided into various subnets within each class.