Lion Cipher Lab
Subnetting and CIDR made simple
- Foundations
- Beginner
- ~30 min
- Free · no account required
Why it matters
Subnetting is the skill hiding underneath nearly every access-control decision a defender makes. A firewall rule that allows "10.0.0.0/8", a cloud security group scoped to one subnet, a VPN that only trusts a range of addresses, network segmentation that keeps the payment machines away from the guest wifi — all of them are just statements about ranges of IP addresses written in CIDR notation. If you can read what "192.168.1.0/24" means and count how many machines fit in a "/26", those rules stop being magic symbols and become plain sentences you can write and audit. This lab builds that from…
What you'll learn
- reading CIDR notation
- network bits vs host bits
- subnet masks
- counting hosts in a range
- RFC 1918 private ranges
- why segmentation and allowlists use CIDR
Steps in this lab
- Start with the address: an IPv4 is 32 bits in four numbers
- Split the address: network bits vs host bits, and the mask
- CIDR notation: the /24 that says where the line falls
- Worked example 1: what does 192.168.1.0/24 actually cover?
- Worked example 2: compute how many hosts a /26 holds
- The private ranges: RFC 1918 and why they matter
- Check your work with a free tool: ipcalc
- Why this is the skill behind firewall rules and segmentation