IP Subnet Calculator

Calculate network ranges and plan your IP addressing scheme

IP Subnet Calculator

How Subnetting Works

Subnetting divides a large network into smaller, manageable subnetworks. Here's how it works:

Network Portion: Identifies the specific network
Host Portion: Identifies individual devices within the network
Subnet Mask: Determines the boundary between network and host bits
Wildcard Mask: Inverse of subnet mask, used in some routing protocols

The calculator performs bitwise AND operations between the IP address and subnet mask to determine the network address, then calculates all other subnet parameters.

Understanding CIDR Notation

CIDR notation simplifies subnet representation by showing only the number of network bits:

Common CIDR Values

/8: 255.0.0.0 (16M hosts)
/16: 255.255.0.0 (65K hosts)
/24: 255.255.255.0 (254 hosts)
/25: 255.255.255.128 (126 hosts)
/26: 255.255.255.192 (62 hosts)
/27: 255.255.255.224 (30 hosts)
/28: 255.255.255.240 (14 hosts)
/30: 255.255.255.252 (2 hosts)

Binary Representation

Each bit in the subnet mask represents a power of 2:

11111111 = 255 (8 network bits)
11111110 = 254 (7 network bits)
11111100 = 252 (6 network bits)
11111000 = 248 (5 network bits)
11110000 = 240 (4 network bits)

Common Subnet Configurations

Small Office/Home Networks

192.168.1.0/24: Standard home router setup (254 devices)
192.168.0.0/24: Alternative home network range
10.0.0.0/24: Small business network

Enterprise Networks

10.0.0.0/16: Large corporate network (65K devices)
172.16.0.0/16: Medium enterprise network
10.1.0.0/24: Department-specific subnet

Point-to-Point Links

/30 subnets: Router-to-router connections (2 usable IPs)
/31 subnets: Modern point-to-point links (RFC 3021)

Network Planning Tips

Best Practices

Plan for future growth - don't make subnets too small
Use consistent addressing schemes across your network
Document your IP address assignments
Reserve ranges for different device types (servers, printers, etc.)
Use private IP ranges (10.x.x.x, 172.16-31.x.x, 192.168.x.x)

Subnet Design Considerations

Security: Separate sensitive systems into different subnets
Performance: Reduce broadcast domains with smaller subnets
Management: Group similar devices for easier administration
Scalability: Leave room for network expansion

Common Mistakes to Avoid

Making subnets too small for future needs
Overlapping subnet ranges
Not documenting network changes
Using public IP ranges for internal networks
Forgetting to account for network and broadcast addresses

Frequently Asked Questions

What is a subnet 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 individual hosts within that network.

What does CIDR notation mean?

CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number (e.g., /24) to indicate how many bits are used for the network portion. /24 means the first 24 bits are for the network, leaving 8 bits for hosts.

Why can't I use the network and broadcast addresses?

The network address (first IP) identifies the network itself, while the broadcast address (last IP) is used to send messages to all devices in the network. These are reserved and cannot be assigned to individual devices.

How do I choose the right subnet size?

Consider your current needs plus future growth. A /24 subnet provides 254 usable addresses, /25 provides 126, /26 provides 62, etc. Choose based on the number of devices you need to support.

IP Subnet Calculator