Subnet Mask Calculator & CIDR Cheat Sheet 🛠️
Stop doing mental binary. Get instant specs for /8 through /32 subnets.
"How many hosts in a /26?" "What is the broadcast address for this IP?" This tool gives network engineers and sysadmins the answers they need without the math fatigue.
💡 What You Can Do
Whether you’re architecting AWS VPCs, configuring a home lab, or writing firewall rules, use this tool to streamline your workflow:
- Design VPCs: Find the right prefix length for your cloud subnets.
- Configure Routers: Generate subnet or wildcard masks and copy them directly to your config.
- Audit Networks: Instantly verify if a specific IP falls within a given range.
📘 Pro Tips
- Search Faster: Use the search bar in the Cheat Sheet tab to filter for specific values like "255.255" or "/29."
- One-Click Copy: Click any value in the table to copy it to your clipboard.
- Calculate Anywhere: Switch to the calculator tab, enter an IP and CIDR, and get the Network ID, Broadcast, and Host Range immediately.
- Identify Classes: Use the quick reference guide at the top to distinguish between Class A, B, and C ranges.
🧐 FAQ
Q. Why is the usable host count "-2"? A. Every standard subnet reserves the first address (Network Address) and the last address (Broadcast Address). Usable Hosts = (2 ^ host_bits) - 2.
Q. How are /31 and /32 handled? A. /31 is used for point-to-point links (2 hosts, no separate network/broadcast), while /32 represents a single host (often used for loopback interfaces).
Q. Is my data secure? A. Yes. All calculations run locally in your browser via JavaScript. Your IP addresses and network configurations are never sent to a server.
📚 Quick Reference
- CIDR (Classless Inter-Domain Routing): The modern standard for efficient IP allocation, replacing the "Classful" system in 1993.
- Wildcard Masks: The inverse of a subnet mask, commonly used in Cisco OSPF and ACL configurations.
- Private Ranges (RFC 1918):
- 10.0.0.0/8
- 172.16.0.0/12
- 192.168.0.0/16