With a /19 subnet mask, how many usable host addresses are available in the subnet?

With a /19 subnet mask, how many usable host addresses are available in the subnet?

• A. 8190
• B. 4096
• C. 8192
• D. 2048

Answer: (A)

Counting usable hosts in a subnet comes from how many bits are left for hosts. A /19 leaves 13 bits for hosts (32 total bits minus 19). So there are 2^13 = 8192 total addresses in that subnet. But the network address and the broadcast address aren’t usable for hosts, so you subtract 2, giving 8190 usable host addresses. For some context, a /19 uses the mask 255.255.224.0, and the subnet size steps in the third octet by 32. As a quick contrast, 4096 would come from 2^12 host bits (a /20), 8192 is the total address count in the subnet, and 2048 comes from 2^11 host bits (a /21).

Counting usable hosts in a subnet comes from how many bits are left for hosts. A /19 leaves 13 bits for hosts (32 total bits minus 19). So there are 2^13 = 8192 total addresses in that subnet. But the network address and the broadcast address aren’t usable for hosts, so you subtract 2, giving 8190 usable host addresses.

For some context, a /19 uses the mask 255.255.224.0, and the subnet size steps in the third octet by 32. As a quick contrast, 4096 would come from 2^12 host bits (a /20), 8192 is the total address count in the subnet, and 2048 comes from 2^11 host bits (a /21).