What determines how many hosts can be on a subnet?

The number of hosts that can be accommodated on a subnet is directly determined by the subnet mask. The subnet mask specifies which portion of the IP address is designated as the network part and which portion is available for host addresses.

In an IPv4 address, for example, the subnet mask divides the address into a network address and a host address. The number of bits allocated for the host portion allows for a certain number of unique combinations, which translates into the number of possible hosts that can be assigned within that subnet. Specifically, the formula to calculate the maximum number of hosts is 2 raised to the power of the number of bits available for hosts, minus 2 (to account for the network and broadcast addresses which cannot be assigned to hosts).

Thus, the subnet mask is fundamental in determining the size of the subnet and therefore significantly influences the number of hosts that can be connected within that subnet. This is why the correct answer to the question focuses on the importance of the subnet mask in network design and management.