Answer: A fully qualified domain name (FQDN) can contain up to 255 characters.
Step-by-step explanation:
Each label in an FQDN can contain up to 63 characters, and the total number of labels in an FQDN can be up to 127. However, some systems may impose a shorter limit on the length of an FQDN. For example, Windows systems typically limit the length of an FQDN to 15 characters.
The characters that can be used in an FQDN are:
Letters: a-z, A-Z
Numbers: 0-9
Hyphens: "-"
Other characters, such as spaces, underscores, and periods, are not allowed in FQDNs.
Here is an example of an FQDN:
www.example.com
This FQDN has three labels: www, example, and com. The www label is the host name, and the example and com labels are the domain names. The total length of this FQDN is 15 characters, which is within the maximum limit of 255 characters.