How many hosts can be configured using a subnet mask 255.255.255.248?

Concept

In IPv4 a subnet mask splits an address into a network portion (the 1-bits) and a host portion (the 0-bits). The number of distinct addresses in a subnet is 2 raised to the number of host bits; of these, two are reserved — the all-zeros address is the network ID and the all-ones address is the broadcast — so the count of usable (configurable) hosts is 2h − 2, where h is the number of host bits.

Application

1. Write the last octet of the mask in binary: 248 = 11111000. The first three octets are 255 (all 1-bits), so every host bit lies in the last octet.

2. Count the 0-bits (host bits): 11111000 has three trailing zeros, so h = 3.

3. Total addresses in the subnet = 23 = 8.

4. Subtract the two reserved addresses (network + broadcast): usable hosts = 8 − 2 = 6.

Cross-check

This mask is a /29 (32 − 3 = 29 network bits). A /29 is the standard small block that yields 6 usable host addresses — a common allocation for point-to-multipoint links and tiny LAN segments — which confirms the result.