How many addresses are available in a CIDR /20?

In CIDR (Classless Inter-Domain Routing), the notation /20 indicates that the first 20 bits of the IP address are designated for the network part, leaving the remaining bits for host addresses. An IPv4 address is 32 bits in total, which means that for a /20 CIDR block, there are 12 bits available for host addresses (32 - 20 = 12).

To calculate the number of possible addresses, you can use the formula (2^{\text{number of host bits}}). In this case, you have:

[2^{12} = 4096]

However, in every subnet, two addresses are reserved. One is for the network address (which identifies the subnet itself) and the other is for the broadcast address (which is used to communicate with all devices on that subnet). Therefore, to find the number of usable addresses for hosts, subtract these two reserved addresses from the total:

[4096 - 2 = 4094]

This means that in a /20 CIDR block, there are actually 4094 usable addresses available for hosts.

The initially provided answer of 4092 might have an error, as it does not account for the proper subtraction based on