Introduction of Classful IP Addressing
Last Updated :
14 Jan, 2025
An IP address is an address that has information about how to reach a specific host, especially outside the LAN. An IP address is a 32-bit unique address having an address space of 232.
Classful IP addressing is a way of organizing and managing IP addresses, which are used to identify devices on a network. Think of IP addresses like street addresses for houses; each device on a network needs its unique address to communicate with other devices. In this article, we will discuss Classful IP addresses, and their types in detail.
Classful IP Addressing
Classful IP addressing is an obsolete method for allocating IP addresses and dividing the available IP address space across networks. It was used from 1981 to 1993 until the introduction of CIDR (Based on Prefixes rather than classes). Classful method categorizes IP addresses into five classes (A, B, C, D, and E), each defined by the first few bits of the address and serving specific ranges of purposes. The functionality of classful networking also extended to ease of configuration. Network administrators could set up networks with default subnet masks without the need for detailed subnetting strategies, which was particularly beneficial in less complex networking environments.
IPV4 Address
An IPv4 address is a unique number assigned to every device that connects to the internet or a computer network. It's like a home address for your computer, smartphone, or any other device, allowing it to communicate with other devices.
- Format: An IPv4 address is written as four numbers separated by periods, like this: 192.168.1.1. Each number can range from 0 to 255.
- The IPv4 address is divided into two parts: NID (Network ID) = 8bit, and HID (Host ID) = 24bit. So there are 28 which is 256 total networks created and 224 which is 16M Host per network.
- Purpose: The main purpose of an IPv4 address is to identify devices on a network and ensure that data sent from one device reaches the correct destination.
- Example: When you type a website address into your browser, your device uses the IPv4 address to find and connect to the server where the website is hosted.
There are two notations in which the IP address is written, dotted decimal and hexadecimal notation.
Dotted Decimal Notation
Some points to be noted about dotted decimal notation:
- The value of any segment (byte) is between 0 and 255 (both included).
- No zeroes preceding the value in any segment (054 is wrong, 54 is correct).
Dotted Decimal NotationHexadecimal Notation
Need For Classful Addressing
- Classful addressing provided a straightforward method to allocate and manage IP addresses based on fixed classes, simplifying the administrative burden associated with IP address distribution.
- Network equipment of the time, such as routers, could be more easily programmed to handle a limited number of fixed classes, speeding up the routing process because the class of an address could be quickly identified from its first few bits.
- While it did have limitations, classful addressing allowed for scaling of networks within the bounds of each class size. Larger networks could use a Class A or B address, and smaller networks could operate efficiently within a Class C subnet.
- By standardizing address ranges, classful addressing facilitated the implementation of uniform network protocols, which was important for the interoperability of network devices across different networks and platforms.
- Classful addressing was a cost-effective solution that supported the early expansion of the Internet by avoiding the need for complex subnetting schemes that require additional computing resources and more sophisticated network management tools.
Classes of IP Addressing
The 32-bit IP address is divided into five sub-classes. These are given below:
- Class A
- Class B
- Class C
- Class D
- Class E
Each of these classes has a valid range of IP addresses. Classes D and E are reserved for multicast and experimental purposes respectively. The order of bits in the first octet determines the classes of the IP address.
The class of IP address is used to determine the bits used for network ID and host ID and the number of total networks and hosts possible in that particular class. Each ISP or network administrator assigns an IP address to each device that is connected to its network.
Classful Addressing Note:
- IP addresses are globally managed by Internet Assigned Numbers Authority (IANA) and Regional Internet Registries (RIR).
- While finding the total number of host IP addresses, 2 IP addresses are not counted and are therefore, decreased from the total count because the first IP address of any network is the network number and whereas the last IP address is reserved for broadcast IP.
Occupation of The Address Space In Classful AddressingClass A
IP addresses belonging to class A are assigned to the networks that contain a large number of hosts.
- The network ID is 8 bits long.
- The host ID is 24 bits long.
The higher-order bit of the first octet in class A is always set to 0. The remaining 7 bits in the first octet are used to determine network ID. The 24 bits of host ID are used to determine the host in any network. The default subnet mask for Class A is 255.x.x.x. Therefore, class A has a total of:
- 224 - 2 = 16,777,214 host ID
IP addresses belonging to class A ranges from 0.0.0.0 - 127.255.255.255.
Class AClass B
IP address belonging to class B is assigned to networks that range from medium-sized to large-sized networks.
- The network ID is 16 bits long.
- The host ID is 16 bits long.
The higher-order bits of the first octet of IP addresses of class B are always set to 10. The remaining 14 bits are used to determine the network ID. The 16 bits of host ID are used to determine the host in any network. The default subnet mask for class B is 255.255.x.x. Class B has a total of:
- 214 = 16384 network address
- 216 - 2 = 65534 host address
IP addresses belonging to class B ranges from 128.0.0.0 – 191.255.255.255.
Class BClass C
IP addresses belonging to class C are assigned to small-sized networks.
- The network ID is 24 bits long.
- The host ID is 8 bits long.
The higher-order bits of the first octet of IP addresses of class C is always set to 110. The remaining 21 bits are used to determine the network ID. The 8 bits of host ID are used to determine the host in any network. The default subnet mask for class C is 255.255.255.x. Class C has a total of:
- 221 = 2097152 network address
- 28 – 2 = 254 host address
IP addresses belonging to class C range from 192.0.0.0 – 223.255.255.255.
Class CClass D
IP address belonging to class D is reserved for multi-casting. The higher-order bits of the first octet of IP addresses belonging to class D is always set to 1110. The remaining bits are for the address that interested hosts recognize.
Class D does not possess any subnet mask. IP addresses belonging to class D range from 224.0.0.0 – 239.255.255.255.
Class DClass E
IP addresses belonging to class E are reserved for experimental and research purposes. IP addresses of class E range from 240.0.0.0 – 255.255.255.255. This class doesn’t have any subnet mask. The higher-order bits of the first octet of class E are always set to 1111.
Class ERange of Special IP Addresses
169.254.0.0 – 169.254.0.16 : Link-local addresses
127.0.0.0 – 127.255.255.255 : Loop-back addresses
0.0.0.0 – 0.0.0.8: used to communicate within the current network.
Rules for Assigning Host ID
Host IDs are used to identify a host within a network. The host ID is assigned based on the following rules:
- Within any network, the host ID must be unique to that network.
- A host ID in which all bits are set to 0 cannot be assigned because this host ID is used to represent the network ID of the IP address.
- Host ID in which all bits are set to 1 cannot be assigned because this host ID is reserved as a broadcast address to send packets to all the hosts present on that particular network.
Rules for Assigning Network ID
Hosts that are located on the same physical network are identified by the network ID, as all host on the same physical network is assigned the same network ID. The network ID is assigned based on the following rules:
- The network ID cannot start with 127 because 127 belongs to the class A address and is reserved for internal loopback functions.
- All bits of network ID set to 1 are reserved for use as an IP broadcast address and therefore, cannot be used.
- All bits of network ID set to 0 are used to denote a specific host on the local network and are not routed and therefore, aren’t used.
Structure of Classful Addressing
In the above table No. of networks for class A should be 127. (Network ID with all 0 s is not considered)
Problems With Classful Addressing
The problem with this classful addressing method is that millions of class A addresses are wasted, many of the class B addresses are wasted, whereas, the number of addresses available in class C is so small that it cannot cater to the needs of organizations. Class D addresses are used for multicast routing and are therefore available as a single block only. Class E addresses are reserved.
Since there are these problems, Classful networking was replaced by Classless Inter-Domain Routing (CIDR) in 1993. We will be discussing Classless addressing in the next post.
- The network ID is 24 bits long.
- The host ID is 8 bits long.
- 221 = 2097152 network address
- 28 - 2 = 254 host address
- Within any network, the host ID must be unique to that network.
- Host ID in which all bits are set to 0 cannot be assigned because this host ID is used to represent the network ID of the IP address.
- Host ID in which all bits are set to 1 cannot be assigned because this host ID is reserved as a broadcast address to send packets to all the hosts present on that particular network.
- The network ID cannot start with 127 because 127 belongs to the class A address and is reserved for internal loopback functions.
- All bits of network ID set to 1 are reserved for use as an IP broadcast address and therefore, cannot be used.
- All bits of network ID set to 0 are used to denote a specific host on the local network and are not routed and therefore, aren't used.
Classful and Classless Addressing
Here is the main difference between Classful and Classless Addressing:
| Parameter | Classful Addressing | Classless Addressing |
|---|
| Basics | In Classful addressing IP addresses are allocated according to the classes- A to E. | Classless addressing came to replace the classful addressing and to handle the issue of rapid exhaustion of IP addresses. |
| Practical | It is less practical. | It is more practical. |
| Network ID and Host ID | The changes in the Network ID and Host ID depend on the class. | There is no such restriction of class in classless addressing. |
| VLSM | It does not support the Variable Length Subnet Mask (VLSM). | It supports the Variable Length Subnet Mask (VLSM). |
| Bandwidth | Classful addressing requires more bandwidth. As a result, it becomes slower and more expensive as compared to classless addressing. | It requires less bandwidth. Thus, fast and less expensive as compared to classful addressing. |
| CIDR | It does not support Classless Inter-Domain Routing (CIDR). | It supports Classless Inter-Domain Routing (CIDR). |
| Updates | Regular or periodic updates | Triggered Updates |
| Troubleshooting and Problem detection | Troubleshooting and problem detection are easy than classless addressing because of the division of network, host and subnet parts in the address. | It is not as easy compared to classful addressing. |
| Division of Address | | |
Conclusion
Classful IP addressing, with its categorization into classes like A, B, and C, was a fundamental method in early networking. It organized IP addresses based on network size but faced limitations in flexibility and efficient use of address space. The development of CIDR addressed these issues by allowing more precise control over subnetting and optimizing address allocation.
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