What is the netmask for a CIDR /28 subnet?

A CIDR (Classless Inter-Domain Routing) notation of /28 indicates that the first 28 bits of the subnet mask are set to 1, and the remaining bits are set to 0. This means that the subnet mask will consist of 28 bits for the network part and 4 bits for the host part, as there are a total of 32 bits in an IPv4 address.

To determine the netmask corresponding to /28, you convert the 28 bits set to 1 into decimal format. The binary representation of the netmask is:

11111111.11111111.11111111.11110000

Breaking it down into octets:

• The first octet (11111111) is 255.
• The second octet (11111111) is also 255.
• The third octet (11111111) is again 255.
• The fourth octet (11110000) results in 240 in decimal.

Thus, the netmask for a /28 subnet is 255.255.255.240, which correctly identifies the network portion of the IP address, leaving 16 possible IP addresses for hosts (2^4 = 16,