CIDR Subnetting Network Online Calculator 2026
CIDR stands for “Classless Inter-Domain Routing” and is a method for assigning IP addresses and managing IP routes. It was developed to improve the efficiency of IP address space utilization and support Internet growth. CIDR replaced the older system of IP address classes (A, B, C) and enables more flexible address allocation.
Fundamentals of CIDR
In the CIDR system, an IP address is specified along with a subnet mask that indicates how the network is segmented. The notation typically looks like this: IP address/subnet prefix. The subnet prefix determines how many bits of the address represent the network and how many bits identify specific hosts within that network.
IP Addresses
An IP address is a 32-bit number, normally represented as four octets (groups of 8 bits), separated by dots.
For example: 192.168.1.1
Subnet Prefix (Subnet Mask)
The subnet prefix specifies how many bits of the IP address are reserved for the network. The remaining bits are used for host addresses within that network. A subnet mask looks like this, for example: 255.255.255.0, which corresponds to a prefix of /24. This means the first 24 bits of the address identify the network, and the last 8 bits are used to identify individual hosts within that network.
CIDR Examples:
Let’s walk through some CIDR network examples:
Example 1: /24 Network
IP address: 192.168.1.0/24 Subnet mask: 255.255.255.0
Meaning: The first 24 bits (192.168.1) identify the network, and the last 8 bits can be used to identify hosts (1 to 254).
Number of Possible Hosts:
2^8 - 2 = 254 (The -2 accounts for the network address and broadcast address, which cannot be used as host addresses.)
CIDR Network Example 2: /30 Network
IP address: 192.168.1.4/30 Subnet mask: 255.255.255.252
Meaning: The first 30 bits (192.168.1.4) identify the network, and the last 2 bits are used to identify hosts.
Number of possible hosts: 2^2 - 2 = 2
Steps to Understanding CIDR
Understand IP address structure: Each IP address consists of a network portion and a host portion, based on the subnet mask or prefix.
Learn how to interpret subnet masks: A subnet mask divides the IP address into network and host portions. The higher the prefix (e.g., /24), the larger the network portion.
Calculate the number of hosts in a subnet: The formula 2^(32 - prefix) - 2 can be used to calculate the number of available hosts.
Subnetting and Supernetting:
Dividing a network into smaller subnets (subnetting) or combining multiple networks into a larger network (supernetting) for better management.
Practical examples: Practice with different prefixes and IP addresses to get a feel for how CIDR is applied in the real world.
CIDR Online Calculator
Enter your network address here: Note: External link
Subnetting and Supernetting
Subnetting and supernetting are two techniques used in IP networks to improve the efficiency of address allocation and organize network structure. Both techniques work with CIDR (Classless Inter-Domain Routing) to enable more flexible network designs. Here we explore both concepts more deeply and explain them with examples.
Subnetting
Subnetting is the process of dividing an IP network into smaller, logically separate networks. This is achieved by extending the subnet mask (that is, increasing the prefix) to use more bits for network addressing and fewer for host addressing. This is useful for organizing internal networks, reducing network traffic, and improving security.
Example 1: Subnetting a /24 Network
Suppose you have a network with the address 192.168.1.0/24, which means you have 256 addresses (1 network address, 254 usable host addresses, and 1 broadcast address).
If your goal is to divide this network into 4 smaller subnets, you would increase the prefix.
New prefix: /26 (since 2^2 = 4 subnets and 24 + 2 = 26)
Subnet mask: 255.255.255.192 (the last 6 bits are used for host addresses, 2^6 = 64 addresses per subnet)
Possible Subnets:
Subnet 1: 192.168.1.0/26 (addresses 192.168.1.1 to 192.168.1.62) Subnet 2: 192.168.1.64/26 (addresses 192.168.1.65 to 192.168.1.126) Subnet 3: 192.168.1.128/26 (addresses 192.168.1.129 to 192.168.1.190) Subnet 4: 192.168.1.192/26 (addresses 192.168.1.193 to 192.168.1.254)
Supernetting
Supernetting, also known as “Route Aggregation” or “Classless Inter-Domain Routing (CIDR)”, is the process of combining multiple networks or subnets into a larger network. This is achieved by shortening the subnet mask (that is, reducing the prefix). Supernetting is primarily used to reduce the number of routes in the routing table and improve the efficiency of routing across the Internet.
Supernetting Example 2:
Supernetting Four /24 Networks
Suppose you have four adjacent /24 networks:
- 192.168.0.0/24
- 192.168.1.0/24
- 192.168.2.0/24
- 192.168.3.0/24
You can combine these four networks into a single /22 network:
Supernet: 192.168.0.0/22 Subnet mask: 255.255.252.0 (the last 10 bits are used for host addresses, 2^10 = 1024 addresses)
Key Points
Subnetting increases the number of networks while decreasing the number of hosts per network. It is useful for detailed network organization and security.
Supernetting decreases the number of networks by combining them into larger blocks, which simplifies routing but offers less granularity and control at the individual network level.
Both techniques require careful planning to be effective and avoid wasting address space.