Question 1

What is a subnet calculator?

Accepted Answer

It divides an IP network into subnets and shows the network address, broadcast address, host range and how many devices each subnet can hold.

Question 2

What is the difference between total addresses and usable hosts?

Accepted Answer

The total counts every address in the block; the usable count excludes the network and broadcast addresses — except for /31 links (RFC 3021), where both addresses are usable.

Question 3

Why show a wildcard mask too?

Accepted Answer

A wildcard mask is the bitwise inverse of the subnet mask. Routers and ACL rules (such as Cisco access lists) use wildcard masks rather than subnet masks.