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This IP Calculator has IPv4 and IPv6 modules. IPv4 has both CIDR and VLSM Calculator (Subnet Calculator).
Subnet Calculator is network designer tool, where you can enter total number of hosts per subnet, and it returns complete network design.
IP Calculator has CIDR and VLSM Subnetting Tutorial. Simplest, easiest and quickest way to learn subnetting.
IP Calculator also has CIDR and VLSM Practice modules. This practice module also explains the answers. You can master subnetting practice using this wonder tool.
Binary Calculator and converter tool is also available.