Subnets

What this IP subnetting interview question tests

This is a medium-difficulty networking question that appears in infrastructure and systems interviews. It tests whether you can work backwards from a subnet mask to understand how many distinct subnets can be carved out of a classful address space, and how the bits are allocated between the network, subnet, and host portions.

To solve questions like this, you need to understand CIDR notation, how subnet masks partition an address, and how to count available subnets given a mask length. The question rewards careful bit-counting and clarity about which bits are fixed by the original allocation versus which are variable for subnetting purposes.

• Classful vs. classless IP addressing
• Subnet mask notation and bit representation
• Network, subnet, and host bit boundaries
• Calculating subnet counts from prefix lengths