IPv4 Subnet Calculator
N/A
N/A
255.255.255.0
254
0.0.0.255
Understanding IPv4 Subnet Calculations: Step-by-Step Example
Example Scenario
Let's calculate subnet information for IP address 192.168.1.100 with a /24 subnet mask.
1. Network Address Calculation
Process: Perform a bitwise AND operation between the IP address and subnet mask
IP Address: 192.168.1.100 (11000000.10101000.00000001.01100100)
Subnet Mask: 255.255.255.0 (11111111.11111111.11111111.00000000)
Network Addr: 192.168.1.0 (11000000.10101000.00000001.00000000)
Explanation: The subnet mask of /24 means the first 24 bits are network bits. All host bits (the last 8 bits) are set to 0 to get the network address.
2. Broadcast Address Calculation
Process: Set all host bits to 1 in the network address
Network Addr: 192.168.1.0 (11000000.10101000.00000001.00000000)
Host Bits: Set last 8 bits to 1
Broadcast: 192.168.1.255 (11000000.10101000.00000001.11111111)
Explanation: For a /24 network, the last octet represents the host portion. Setting all these bits to 1 gives us 255 for the last octet.
3. Usable Address Range
Process: Determine the range of addresses that can be assigned to hosts
First Usable: 192.168.1.1 (Network Address + 1)
Last Usable: 192.168.1.254 (Broadcast Address - 1)
Total Usable: 254 addresses (2^8 - 2)
Explanation:
- Total addresses: 2^8 = 256
- Reserved addresses: Network (x.x.x.0) and Broadcast (x.x.x.255)
- Usable addresses: 256 - 2 = 254 addresses
4. Additional Network Information
Subnet Mask: 255.255.255.0
Wildcard Mask: 0.0.0.255
CIDR Notation: 192.168.1.0/24
Binary Subnet Mask: 11111111.11111111.11111111.00000000
Key Points
- This is a Class C network (first octet between 192 and 223)
- Commonly used for small to medium-sized local networks
- Perfect for networks requiring up to 254 hosts
- Part of private IP address space (192.168.0.0/16)
5. Common Use Cases
- Home networks and small offices
- Individual departments within a larger network
- Guest Wi-Fi networks
- IoT device networks
Best Practices: When implementing this subnet:
- Reserve lower addresses for network infrastructure (routers, switches)
- Consider using DHCP for automatic address assignment (e.g., 192.168.1.100-200)
- Document static IP assignments to prevent conflicts
Questions & Answers
- An IPv4 Subnet Calculator is a tool that helps network administrators calculate and plan IP address ranges within a network. It determines important network information like usable host addresses, broadcast addresses, and subnet masks based on an IP address and CIDR notation.
- CIDR (Classless Inter-Domain Routing) notation is a compact method of specifying IP addresses and their routing prefix. It's written as an IP address followed by a forward slash and a number (e.g., 192.168.1.0/24), where the number represents the count of leading 1 bits in the routing prefix mask.
- A subnet mask is a 32-bit number that divides an IP address into network and host portions. It determines which part of the IP address identifies the network and which part identifies the host. For example, 255.255.255.0 is a common subnet mask.
- Usable addresses are the IP addresses within a subnet that can be assigned to network devices. The total number of usable addresses is always less than the total subnet size because two addresses are reserved: the network address (first address) and the broadcast address (last address).
- A wildcard mask is the inverse (bitwise NOT) of a subnet mask. It's commonly used in access control lists (ACLs) and routing protocols. While subnet masks use 1s to show network bits, wildcard masks use 0s to show which bits must match exactly.
- A network address is the first address in a subnet, which identifies the network itself. It's calculated by performing a bitwise AND operation between an IP address and its subnet mask. Network addresses cannot be assigned to devices.
- A broadcast address is the last address in a subnet, used to send data to all devices in that subnet. It's calculated by setting all host bits to 1. Like the network address, it cannot be assigned to devices.
- Choose your CIDR prefix based on how many hosts you need in your network. For example, /24 gives you 254 usable addresses, /25 gives 126, and /26 gives 62. The smaller the number after the slash, the larger the network.
- The first address (network address) identifies the network itself, while the last address (broadcast address) is used to send packets to all hosts in the network. These addresses are reserved by network protocols and cannot be assigned to devices.
- IP address classes (A, B, C, D, E) were the original method of dividing IP address space. Class A uses /8 prefix, B uses /16, and C uses /24. However, this system has largely been replaced by CIDR for more flexible network planning.