Wie in Kodieren Punycode Domains

问题

You haben ein domain Name mit non-ASCII Zeichen (e.g., Bücher.com) und brauchen its Punycode form für DNS lookups.

Voraussetzungen

• Understanding of DNS
• Familiarity with Unicode

Schritte

1. 1. Split the domain into labels

   Separate the domain name at each dot. Punycode is applied per-label, not to the whole domain. The TLD and each subdomain label are processed independently.

   Eingabe

   Bücher.com

   输出

   labels: ['Bücher', 'com']

2. 2. Encode each non-ASCII label to Punycode

   For each label containing non-ASCII characters, prefix the Punycode output with xn-- and append the encoded form. ASCII-only labels like 'com' remain unchanged. The encoding maps Unicode code points to a compact ASCII representation.

   Eingabe

   Bücher

   输出

   xn--Bcher-kva

3. 3. Reassemble and verify

   Join the encoded labels with dots. Use the result for DNS resolution. Most browsers and DNS libraries perform this conversion automatically, but APIs and logs often show the Punycode form.

   Eingabe

   xn--Bcher-kva.com

   输出

   resolves to the same server as Bücher.com

Erwartetes Ergebnis

Ein ASCII-nur domain Name (ACE form) das DNS resolvers kann Abfrage, equivalent in der original IDN.

Häufige Fehler

Encoding the entire domain as one label

Split on dots first. Only labels with non-ASCII characters get the xn-- prefix.

Case is lost in conversion

Punycode preserves the case of the first character. Use a standards-compliant encoder to handle case correctly.

Troubleshooting指引

• If DNS lookup fails, verify the xn-- prefix is present and lowercase.
• Some older resolvers do not support IDN. Use the Punycode form directly in those cases.

Sicherheitsgrenzen

• Punycode enables homograph attacks (e.g., аpple.com using Cyrillic а). Always display the Unicode form to users and warn about mixed-script domains.