DNS on Windows 2000, Second Edition

Unicode Character Support

The Microsoft DNS Server allows any character from the Unicode character set to be used in a domain name. These characters are represented in UTF-8, a particular method of encoding Unicode characters.^[49] The vast majority of DNS domain names are represented with a subset of the ASCII character set: alphanumeric characters (i.e., the uppercase and lowercase letters A-Z and the digits 0-9) and the hyphen. In fact, the DNS specification has always permitted any binary value to be used in domain names, though RFC 1035—one of the core RFCs that define DNS—recommends that domain names be limited to the characters just listed to avoid problems using the domain names with other protocols. For example, the Internet standards dealing with valid hostname syntax (RFCs 952 and 1123) restrict hostnames to the same ASCII alphanumeric subset. Since this hostname syntax is referenced in Internet standards for electronic mail, domain names used in email addresses must use this same limited syntax.

Until Windows 2000, however, networking in Microsoft operating systems was based on NetBIOS, which has more liberal hostname-syntax rules than strict alphanumerics and the hyphen. As we mentioned earlier in this chapter, limited punctuation is allowed in NetBIOS names, as well. Since DNS is the protocol used to name hosts in Windows 2000, sites that upgrade can run into trouble with hosts named according to NetBIOS syntax rules that are no longer valid according to the accepted ...