Free, interactive networking tools from Practical Networking — CIDR & subnet calculators, subnetting practice, and TCP congestion-control visualizers.

CIDR IP .com

Interactive CIDR/subnet mask slider that visualizes how CIDR notation affects an IP address in binary and decimal.

SubnetIPv4.com

Randomized subnetting practice problems with auto-fill, auto-check, and a full Subnetting Mastery video series.

TCP RTO Calculator

Step-by-step RFC 6298 / Jacobson-Karels TCP Retransmission Timeout calculator.

TCP Reno/Cubic Visualizer

Interactive TCP Reno and Cubic congestion window visualizer with slow start, fast recovery, and congestion avoidance phases.