Quick CIDR Reference
| CIDR | Subnet Mask | Total Hosts | Description |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | Single host |
| /31 | 255.255.255.254 | 2 | Point-to-point |
| /30 | 255.255.255.252 | 4 | Point-to-point links |
| /29 | 255.255.255.248 | 8 | Small subnet |
| /28 | 255.255.255.240 | 16 | Very small network |
| /27 | 255.255.255.224 | 32 | Small network |
| /26 | 255.255.255.192 | 64 | Small network |
| /25 | 255.255.255.128 | 128 | Medium network |
| /24 | 255.255.255.0 | 256 | Class C |
| /16 | 255.255.0.0 | 65,536 | Class B |
| /8 | 255.0.0.0 | 16,777,216 | Class A |
Click any row to use that CIDR value
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Subnetting Fundamentals
Why Subnet?
Subnetting divides large networks into smaller, manageable segments. Benefits include:
- Reduced broadcast traffic (better performance)
- Improved security (segment isolation)
- Simplified troubleshooting
- Efficient IP address allocation
- Better network organization
Common Subnet Sizes
VLSM (Variable Length Subnet Masking)
VLSM allows using different subnet masks within the same network to optimize IP address usage. Instead of using one /24 for all subnets, you can allocate /28 for small departments and /25 for large ones.
Example: Company with 200 Employees
VLSM saves IP addresses by right-sizing subnets to actual needs instead of allocating /24 everywhere.
Practical Applications
Network Design
Plan IP addressing for new networks. Calculate required subnet sizes for different departments, VLANs, or locations. Ensure no overlap and efficient use of address space. Document IP allocation for future reference.
Firewall Configuration
Use CIDR notation in firewall rules and ACLs. The Range Merger helps consolidate rules to reduce rule count, improve performance, and simplify management. Fewer rules = easier troubleshooting.
Route Aggregation
Summarize multiple routes into fewer routing table entries. This reduces router memory usage, speeds up routing lookups, and minimizes BGP update traffic. Essential for large networks and ISPs.
Cloud Networking
Plan VPC/VNet subnets in AWS, Azure, or GCP. Allocate CIDR blocks for different environments (dev, staging, prod), availability zones, and service tiers. Avoid overlaps for VPC peering or VPNs.
Frequently Asked Questions
Common questions about the Subnet Calculator
CIDR (Classless Inter-Domain Routing) notation represents IP addresses and subnet masks compactly. The /24 in 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits for hosts (256 addresses). Common values: /32 = single host, /24 = 256 addresses (Class C), /16 = 65,536 addresses (Class B).
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âšī¸ Disclaimer
This tool is provided for informational and educational purposes only. All processing happens entirely in your browser - no data is sent to or stored on our servers. While we strive for accuracy, we make no warranties about the completeness or reliability of results. Use at your own discretion.