Maximum host count is the number of IPv4 addresses assignable to hosts in a network. It excludes the network address and broadcast address, which are reserved for identifying the network and addressing all hosts. section 7.3.3
Calculate it with 2^y − 2, where y is the number of host bits. A /24 network has eight host bits, so it provides 2^8 − 2 = 254 usable host addresses. section 7.3.3
As the prefix length increases, borrowed bits create more subnets but leave fewer host bits and fewer hosts per subnet:
- Point-to-point links can use /30 with two host addresses or, where valid, /31 with two addresses and no network or broadcast address. section 11.5
