Internet layer Table of Contents Why can't I use the first or last address in a subnet? Why can't I use the first or last address in a subnet? discussion A.B.C.0 (first) is for the subnet identifier. A.B.C.255 is for broadcast. https://superuser.com/questions/1111437/why-cant-i-use-the-first-or-last-address-in-a-subnet