Size, split and summarise subnets. Relevant for CCNA.
Variable-length subnet masking is subnetting applied backwards: start from the hosts you need, or the subnets you need, and find the prefix. The CCNA asks it in several disguises, and all of them come down to powers of two and block sizes.
Subbing covers sizing a subnet for a host count, counting the subnets that fit in a block, finding the nth subnet and the next subnet, borrowing bits for a required number of subnets, splitting a block into equal parts, and summarising contiguous /24s into one route.
Generated by the same code as the app. They change with every release; the app never runs out.
VLSM and route summarisation: Sizing subnets for host counts, carving a block into subnets, finding the nth subnet, and summarising contiguous networks into one route.
You need 50 + 2 = 52 addresses. The smallest power of two at or above 52 is 64 = 2^6, so 6 host bits and a /26.
Four contiguous /24s is 2^2, so free 2 bits: 24 - 2 = /22. The first network, 10.1.4.0, is aligned to a block of 4 in the third octet, so the summary is 10.1.4.0/22.