How is a subnet mask typically written?

• A. As a decimal number
• B. In binary format
• C. With slashes
• D. As four octets separated by periods

Answer: (D)

A subnet mask is typically written as four octets separated by periods, which is a standard representation in the IPv4 addressing scheme. Each octet represents an 8-bit number, allowing for a range from 0 to 255. This format makes it easy to read and understand the structure of the subnet mask, as each octet correlates directly to the binary representation of the mask.

For example, a common subnet mask might be written as "255.255.255.0." This denotes that the first three octets are used for the network portion, indicated by the binary values of 11111111 for each, while the last octet (0) indicates that the host portion comprises the remaining bits.

While subnet masks can be represented in binary format or with CIDR notation (using slashes), the dotted-decimal format remains the most recognizable and widely used in networking contexts. This makes it an ideal choice for various configurations in networking equipment, IP configuration, and documentation.