How to use these tools
Every calculator on this page runs entirely in your browser. Nothing you type is sent to a server, so you can safely paste internal addressing while you plan a change. Pick a tab above, type an address or mask, and results update as you type.
Subnet calculator
Enter any IPv4 address with a prefix length (/27) or a dotted subnet mask (255.255.255.224). You get the network and broadcast addresses, the usable host range, total and usable host counts, the wildcard mask, the address class and whether the address is private (RFC 1918), shared CGNAT space (RFC 6598), loopback or link-local. The binary view highlights network bits and host bits so you can see exactly where the boundary falls — the fastest way to build intuition. If subnetting still feels like magic, read Subnetting Made Simple next.
VLSM planner
Variable Length Subnet Masking lets you carve one block into differently sized subnets so you waste fewer addresses. Enter the parent network and the number of hosts each segment needs. The planner sorts requirements largest-first, aligns every subnet on its natural boundary and shows the remaining free space — the same method you would use on paper during a CCNA exam.
IP converter
Convert between dotted decimal, 32-bit binary, hexadecimal and integer representations. Handy when reading packet captures, firewall logs that store addresses as integers, or building reverse DNS zones.
Wildcard mask calculator
Cisco ACLs and OSPF network statements use wildcard (inverse) masks. Enter a mask or prefix to get the wildcard and ready-to-adapt configuration examples.
Common ports lookup
Search a curated list of well-known TCP and UDP ports used in enterprise networks — management, routing, authentication, monitoring and VPN protocols — with practical security notes. Use it when writing firewall rules, and pair it with our Firewall Hardening Checklist.
Accuracy and limitations
The calculators follow standard IPv4 rules, including RFC 3021 /31 point-to-point links and /32 host routes. They do not yet support IPv6; for IPv6 planning see IPv6 for Network Admins. Always double-check critical changes in a lab, as described in our Disclaimer.