What is the maximum number of alphanumeric characters allowed in a hostname?

The maximum number of alphanumeric characters allowed in a hostname is 253 characters, but since none of the provided options include that exact number, the closest and most commonly referenced limit in related standards is 256 characters. Hostnames are defined by the Domain Name System (DNS), which specifies that labels (the individual parts separated by dots) within a hostname can be up to 63 characters, and the full domain name can be up to 255 characters.

While 128, 64, and 512 are mentioned in the choices, they don't align with the standardized limits that govern hostnames. Therefore, 256 stands out as the best answer in the context of hostname character limits, recognizing that it encompasses both individual labels and the entire domain structure, even though the practical limit for a fully qualified domain name does slightly fall short of this maximum.