Answer: There are 13 usable IP addresses in a /28 subnet.
In a /28 subnet the 28 bits from 32 bits represents the network bits and remaining 4 bits represents the host bits. So, the total number of IP address is 16 IP address. But from the 16 IP address three IP addresses are used for subnet address, gateway address and broadcast address. Hence the usable IP address is 16 – 3 = 13 IP addresses. The IP address in which the four host bits are 0 then, it is subnet address, if the four host bits represents decimal 1 then it represents the gateway address and if the four host bits are 1 i.e., decimal 15 then, it represents the broadcast address. So, these three addresses cannot be used or assigned. Therefore, the remaining usable IP addresses are 13 in a /28 subnet.
Conclusion
From the above discussion we can conclude that in a /28 subnet we have 13 usable IP addresses only. The number of network bits and host bits in a /28 subnet are 28 and 4 bits respectively. The 4 host bits can represent 16 IP address from which three IP addresses are used for representing subnet address, gateway address and broadcast address. The remaining IP addresses are 16 – 3 = 13 IP addresses. Hence, there are 13 usable IP addresses in a /28 subnet.