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We try to use hostheader with the german umlaut ß (sharp s, "Eszett") like www.straße123.de in IIS 10 websites. The hostheader is accepted in IIS, the DNS entry or HOSTS entry on client with punycode is accepted and works.

But regardless if the website is started or stopped, in Firefox I get an error message 400 "Bad Request - Invalid Hostname". Chrome and Edge convert the "ß" to "ss", e.g. www.strasse123.de which is not wanted.

I have no clue how get this running.

StefanK
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  • Does www.xn--strae123-tya.de work, the ASCII-URL? – Lenniey Sep 09 '19 at 14:46
  • You can't add this as hostheader in IIS. When opened in Firefox it's converted to www.straße123.de and results in the error 400. – StefanK Sep 09 '19 at 15:06
  • "Chrome and Edge convert the "ß" to "ss", e.g. www.strasse123.de which is not wanted." DENIC (`.DE` registry) changed its rules on August 2010 see https://www.denic.de/en/faqs/faqs-about-idns-ss/#code-365. `ß` is handled differently in IDNA2003 and IDNA2008, so it depends on which version of the standard each party (client and server) uses. See also https://www.denic.de/en/know-how/idn-domains/ "Things to be Considered for Domains Containing the Letter Eszett (ß)" and its conclusion – Patrick Mevzek Sep 10 '19 at 17:43

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