The hostname shall follow RFC 1035 Host name convention. Note that while upper and lower case letters are allowed in domain names, no significance is attached to the case. That is, two names with the same spelling but different case are to be treated as if identical. The labels must start with a letter or digit, end with a letter or digit, and have as interior characters only letters, digits, and hyphen. There are also some restrictions on the length. Labels must be 63 characters or less. There are up to 4 labels per hostname.