CCNA | P4: IPv4 Addressing | C2: Analyzing Classful IPv4 Networks

Classful addressing was the first method used to allocate IP addresses. It was later replaced by classless addressing, which is more flexible and efficient. However, understanding classful addressing is still important for network administrators and engineers. It’s like learning the basics of a language before diving into the more complex aspects of it.

Lesson Contents

• Classful Addressing
  -Network ID
  -Host ID
• The 5 Classes of IPv4 Addresses
  -Class A
  -Class B
  -Class C
  -Class D
  -Class E
• Key Factors To Analyze Classful IPv4 Networks
• Conclusion

Classful Addressing

Classful addressing is a fascinating method of dividing IP addresses into five classes: A, B, C, D, and E.
Each class has a different range of IP addresses and a different default subnet mask. It’s like a treasure hunt where each class is a new adventure waiting to be explored!

To understand the method used for dividing the IP address in classes, we must first learn the concept of network ID and host ID.

These concepts are used in IP addressing to identify the network and the host to which an IP address belongs. The IP address is divided into two parts: network ID and host ID. The network ID identifies the network to which the host belongs, while the host ID identifies the host within that network. It’s like a secret code that unlocks the mysteries of the internet!

In dotted-decimal representation, an IP address is divided into four octets, and based on which class the IP address belongs to, its octets are further divided into network ID and host ID.

Network ID

The network ID is the fragment of an IP address that classifies the network for a specified host. It tells us which network the host belongs to and is generally comprised of one to up to four octets in dotted-decimal representation.

Host ID

The host ID is the fragment of an IP address that uniquely classifies a host on a specified TCP/IP network. A host ID can be found simply by ANDing the IP address in binary form with its respective default subnet mask (in binary form).

The 5 Classes of IPv4 Addresses

Each class of IP addresses has a unique range of IP addresses and a different default subnet mask. The first bit of the first octet is always set to 0 for Class A, 10 for Class B, 110 for Class C, 1110 for Class D, and 1111 for Class E.

Class A

• Class A is used for large networks and has a range of IP addresses from 0.0.0.0 to 127.255.255.255. The first bit of the first octet is always set to 0, which means that the remaining 7 bits are used to identify the network. The default subnet mask for Class A is 255.0.0.0, which means that the first octet is used to identify the network and the remaining three octets are used to identify the host. Addresses beginning with 0 and 127 are reserved (the latter for loopback).

Class B

• Class B is used for medium-sized networks and has a range of IP addresses from 128.0.0.0 to 191.255.255.255. The first two bits of the first octet are always set to 10, which means that the remaining 14 bits are used to identify the network. The default subnet mask for Class B is 255.255.0.0, which means that the first two octets are used to identify the network and the remaining two octets are used to identify the host.

Class C

• Class C is used for small networks and has a range of IP addresses from 192.0.0.0 to 223.255.255.255. The first three bits of the first octet are always set to 110, which means that the remaining 21 bits are used to identify the network. The default subnet mask for Class C is 255.255.255.0, which means that the first three octets are used to identify the network and the remaining octet is used to identify the host.

Class D

• Class D is used for multicast addresses and has a range of IP addresses from 224.0.0.0 to 239.255.255.255. The first four bits of the first octet are always set to 1110.

Class E

• Class E is reserved for future use and has a range of IP addresses from 240.0.0.0 to 255.255.255.255. The first four bits of the first octet are always set to 1111.

The default subnet mask for each class is based on the number of network bits in the IP address.
For example, a Class A address has 8 network bits and 24 host bits, so the default subnet mask is 255.0.0.0. A Class B address has 16 network bits and 16 host bits, so the default subnet mask is 255.255.0.0. A Class C address has 24 network bits and 8 host bits, so the default subnet mask is 255.255.255.0.

Table summarizing all the classes:

Key Factors To Analyze Classful IPv4 Networks

When analyzing classful IPv4 networks, there are several key facts that you should be aware of.

These include:

• The class of the IP address
• The default subnet mask for the class
• The network address for the IP address
• The broadcast address for the network
• The number of hosts that can be connected to the network

To determine these facts, you need to perform the following steps:

1. Identify the class of the IP address by looking at the first octet of the address. The first octet will tell you which class the address belongs to.
2. Determine the default subnet mask for the class. This will tell you how many network bits and how many host bits are in the address.
3. Calculate the network address for the IP address. This is done by performing a bitwise AND operation between the IP address and the subnet mask.
4. Calculate the broadcast address for the network. This is done by performing a bitwise OR operation between the network address and the inverted subnet mask.
5. Calculate the number of hosts that can be connected to the network. This is done by subtracting 2 from the total number of possible host addresses. The first address is reserved for the network address, and the last address is reserved for the broadcast address.

Conclusion

Analyzing classful IPv4 networks is an important skill for network administrators and engineers. By understanding the basics of classful addressing and how to analyze classful IPv4 networks, you can design and manage networks more effectively. I hope this article has been helpful in providing you with a detailed understanding of classful addressing and how to analyze classful IPv4 networks. If you have any further questions or would like me to write about a specific topic, please let me know.

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