CIDR RANGE CALCULATOR
Practical CIDR skills — decode blocks, check containment, aggregate ranges, and find redundancies in real-world whitelists.
MISSION
Master CIDR notation through four escalating challenges. Start by decoding ranges, then evaluate firewall rules, consolidate vendor whitelists, and audit ACLs for redundant entries.
Every question maps to real-world network administration tasks you will face on the job and on the exam.
PHASES
1. DECODE -- Given a CIDR block, identify the start IP, end IP, subnet mask, and usable host count.
2. CLASSIFY -- Does a given IP fall within a CIDR range? Simulates firewall ACL evaluation.
3. AGGREGATE -- Collapse multiple CIDR blocks into the minimum set. The alignment rule is key.
4. FIND REDUNDANCIES -- Audit a messy ACL and flag entries already covered by broader rules.
REFERENCE
Total addresses = 2^(32 - prefix)
Usable hosts = 2^(32 - prefix) - 2
Subnet mask = first <prefix> bits set to 1
Alignment rule: start address must be divisible by block size
4 phases · 31 scored answers · ~20 minutes