Tools
Free network tools that run in your browser.
CIDR Calculator — CIDR to IP Range
Turn a CIDR block like 10.0.0.0/22 into its first and last address, mask and size, or turn a start–end IP range into the exact CIDR blocks that cover it.
Subnet Calculator
Enter an IPv4 address with a prefix or subnet mask and get the network and broadcast addresses, the usable host range, the masks, and an optional split into smaller subnets.
CSR and Certificate Decoder
Decode a certificate signing request or an X.509 certificate from its PEM text: subject, issuer, validity, alternative names, key and signature algorithm.
DNS Speed Test — Find the Fastest DNS for You
Times DNS-over-HTTPS lookups from your browser to the big public resolvers, five rounds each, so you can see which one is fastest from your connection.
IP Address Converter (Binary, Hex, Integer, IPv6)
Convert an IPv4 address between dotted decimal, a 32-bit integer, hexadecimal and binary, and see its IPv4-mapped IPv6 form.
IPv6 Subnet Calculator
Enter an IPv6 address and prefix to see the network, first and last address, how many /64 subnets fit, the address type, and the compressed and expanded forms.
Random IP and MAC Address Generator
Generate lists of random IPv4 (public, private or any), IPv6 and MAC addresses for test data, documentation and lab setups.
Subnetting Practice: Unlimited Questions with Answers
Random subnetting questions at three difficulty levels, checked instantly, with the block-size method shown step by step. Includes a timed ten-question quiz.
VLSM Calculator
Give a network and the number of hosts each subnet needs; the calculator places right-sized subnets largest first and shows each one's network, mask and usable range.