Last Updated on August 3, 2025 by Arnav Sharma
In the vast and intricate world of networking, understanding the foundational concepts is crucial for anyone looking to navigate this complex domain. At the heart of networking lie several key concepts: IP addresses, subnet masks, subnets, and the classification of networks. These elements work in concert to define, segment, and manage the digital pathways that facilitate our daily internet activities. This blog divesinto these basics, providing a comprehensive overview to enlighten both novices and seasoned professionals.
IP Address
An IP address is a unique identifier assigned to each device on a network, allowing them to communicate with one another. Structured as a 32-bit number, an IPv4 address is divided into two main parts: the network portion and the host portion, underscoring the division between hosts and subnets within the address system. The network portion identifies the network to which a device belongs, while the host portion identifies the specific device within that network. This binary number is commonly represented in decimal form, divided into four octets for easier comprehension, utilizing a total of 32 bits which signifies how an IP address is structured.
Subnet Mask
A subnet mask works hand in hand with an IP address to define the network and host portions of the address. It’s a 32-bit number that masks the IP address, allowing you to identify the network segment and the device segment within the IP address. For example, a subnet mask of 255.255.255.0 indicates that the first 24 bits represent the network portion, leaving the last 8 bits for the host portion.
Example 1: IP Address and Subnet Mask
Consider a device within a local network assigned the IPv4 address 192.168.1.10. This address is part of a larger network, identified by the subnet mask, which is a prime example of how network address translation between different networks occurs. 255.255.255.0. In binary, the IP address is 11000000.10101000.00000001.00001010, and the subnet mask is 11111111.11111111.11111111.00000000.
The subnet mask shows that the first 24 bits (255.255.255) are the network portion, indicating all devices with addresses starting 192.168.1 are on the same network. The last 8 bits (.0) are the host portion, differentiating devices within this network. In this case, .10 identifies our specific device. This network can host up to 254 devices (2^8-2, accounting for the network address and broadcast address).
Address Class and Network Classes
IP addresses are categorized into classes based on the number of bits used for the network portion, reflecting how the address is used for distinguishing between hosts and subnets. Class A addresses use 8 bits for the network portion, allowing for a large number of networks but fewer hosts within each network. Class B addresses use 16 bits for the network portion, balancing the number of networks and hosts. Class C addresses use 24 bits for the network portion, suitable for small networks with a maximum of 254 hosts.
Subnetting
Subnetting is the process of dividing a single physical network into multiple smaller, logical sub-networks (subnets). This is achieved by extending the network portion of the address and reducing the host portion accordingly, a method that also relates to how a network uses its address space. Subnetting allows network administrators to create a hierarchy of networks, improving network performance and security by limiting the size of broadcast domains.
Example 2: Subnetting a Class C Network
A business has been allocated a Class C IP address range, 192.168.5.0/24, with the default subnet mask of 255.255.255.0. The business wants to segment its network into 4 subnets for different departments. To do this, it needs to borrow bits from the host portion to create additional network bits.
By borrowing 2 bits from the host portion, we can create 4 subnets (2^2 = 4), changing our subnet mask to 255.255.255.192 (11111111.11111111.11111111.11000000 in binary). This divides our address space into four subnets, each with 64 addresses (62 usable hosts after excluding the network and broadcast addresses).
Subnets would be:
- Finance:
192.168.5.0/26(usable addresses:192.168.5.1to192.168.5.62) - HR:
192.168.5.64/26(usable addresses:192.168.5.65to192.168.5.126) - IT:
192.168.5.128/26(usable addresses:192.168.5.129to192.168.5.190) - Marketing:
192.168.5.192/26(usable addresses:192.168.5.193to192.168.5.254)
CIDR Notation
Classless Inter-Domain Routing (CIDR) notation is a method for specifying IP addresses and their associated routing prefix. CIDR notation uses a slash (“/”) followed by a number to indicate the number of bits in the network portion of the address. For example, the CIDR notation for a Class C network might be 192.168.1.0/24, indicating that the first 24 bits are used for the network address and effectively showing how a single network can be segmented into multiple subnets.
Example 3: CIDR Notation and Address Classes
A network is using the IP address 10.0.0.0 with a CIDR notation of /16, meaning the subnet mask is 255.255.0.0. This is indicative of a Class B address, where the first 16 bits (255.255) are used for the network portion, and the remaining 16 bits are for hosts. This allows for 65,536 addresses within the network, suitable for a larger organization.
In contrast, a Class C network might use an address like 192.168.1.0/24, with a subnet mask of 255.255.255.0, dedicating 24 bits to the network portion and allowing for 256 addresses, ideal for smaller networks.
Subnets and Network Masks
The creation of subnets involves defining a subnet mask that determines how the IP address space is divided. A Class C subnet mask of 255.255.255.0, for instance, divides the address space into subnets with 256 addresses each, of which 254 can be assigned to hosts (the first and last addresses in each subnet are reserved).
Subnetting Work
Subnetting enables efficient use of IP address space, reduces network traffic, and enhances security. Network administrators use subnet calculators to determine the appropriate subnet mask, number of hosts per subnet, and number of subnets created. By adjusting the subnet mask, administrators can create a network that precisely fits the size and requirements of their organization, whether it’s a small local network or an extensive enterprise network.
Example 4: Subnetting a Large Network
An organization requires 8 subnets from a single physical network with the address 172.16.0.0/16. To create 8 subnets, 3 bits must be borrowed from the host portion (since 2^3 = 8), altering the subnet mask to 255.255.224.0 (11111111.11111111.11100000.00000000 in binary).
This configuration results in 8 subnets, each supporting up to 8,192 addresses (8,190 usable). This demonstrates how subnetting can efficiently manage a large network’s IP address space, tailoring it to an organization’s specific structural needs, making it integral to divide a network into subnets for enhanced manageability.