10. Internationalization Considerations
The AXFR protocol is transparent to the parts of DNS zone content that can possibly be subject to Internationalization considerations. It is assumed that for DNS labels and domain names, the issue has been solved via "Internationalizing Domain Names in Applications (IDNA)" [RFC3490] or its successor(s).
Transparency of AXFR
AXFR operates at the DNS protocol level and treats all DNS resource records as opaque data. It does not interpret or modify the content of DNS labels, domain names, or RR data. Therefore, AXFR itself does not introduce any internationalization issues.
IDNA Compatibility
For zones containing Internationalized Domain Names (IDNs), the domain names are represented in ASCII-compatible encoding (ACE) form using Punycode as specified by IDNA [RFC3490]. AXFR transfers these ACE-encoded names exactly as they appear in the zone, without any special processing.
Example: If a zone contains the domain name xn--bcher-kva.example (the ACE encoding of "bücher.example"), AXFR transfers this name as xn--bcher-kva.example. The AXFR client stores and serves the name in the same ACE-encoded form.
No Special Handling Required
Because AXFR treats DNS names and data as opaque, no special handling is required for internationalized content. AXFR implementations do not need to be aware of IDNA or any other internationalization mechanisms.
Responsibilities of DNS Software
While AXFR itself is transparent to internationalization issues, other components of DNS software (such as zone file parsers, dynamic update processors, and query processors) may need to handle internationalized domain names according to IDNA specifications. These responsibilities are outside the scope of this document.
Future Considerations
If future versions of IDNA or other internationalization mechanisms require changes to how domain names are represented in DNS protocol messages, those changes will apply equally to AXFR. This document does not impose any constraints on future internationalization efforts.