Why does the formula for number of hosts per subnet 2-2 require subtraction two hosts?

The formula for the number of usable hosts per subnet, often written as 2 ⁿ - 2, subtracts two because two IP addresses in each subnet are reserved and not available for assigning to individual hosts:

1. Network Address: The first IP address in a subnet is the network address itself. It identifies the subnet and cannot be assigned to a host. Think of it as the "subnet label."

2. Broadcast Address: The last IP address in a subnet is the broadcast address. It's used to send packets to *all* devices on that subnet simultaneously. Assigning it to a specific host would cause conflicts.

Therefore, you must subtract these two reserved addresses from the total number of addresses (2 ⁿ , where 'n' is the number of bits used for host addressing in the subnet mask) to get the actual number of usable host addresses.