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I'm trying to understand the limitations of International Domain names... can someone explain what I can and can't do?

Can I register a neat domain name like e=mc2.com?

Are any of these symbols permitted: !@#$%^&*()_+?

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Please explain the close vote. There is no rationale behind it being off topic for this forum. DNS and its' administration, operation, and issues is entirely appropriate for serverfault.com –  makerofthings7 Nov 16 '10 at 2:54

4 Answers 4

up vote 7 down vote accepted

Punycode only alters characters at codepoints greater than or equal to 128, therefore the punycode representation of e=mc2 is still e=mc2 which can't be made a valid DNS name.

Unicode is full of homographs, so the obvious thing to try would be to use U+FF1D (Fullwidth Equals Sign), unfortunately thanks to people registering paypal.com there are now controls on what characters are permitted, depending on the TLD/registrar (as another example, the new Russian Cyrillic TLD .рф disallows mixing Cyrillic and Latin character sets). The (currently proposed) RFC 5892 attempts to formalize rules for classifying which characters should be allowed in which cases.

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3  
If you registered a domain name using U+FF1D, people are going to see it and try to type an ASCII equal sign and get an error. The only place this would work is for clickable links and those rarely show the URL since it's the link text that's displayed. I see no point in having a clever URL in an advertisement, for example, that can't be typed in accurately using the local language. –  Dennis Williamson Nov 16 '10 at 14:34

For .com domains, see this page for documentation on which Unicode code points Verisign permit (and prohibit) in domain names.

The general rule is that symbol characters are not permitted.

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Looks like a-z, 0-9, and hyphens are allowed. As well as 1-63 characters long.

http://en.wikipedia.org/wiki/Hostname

http://tools.ietf.org/html/rfc952

http://tools.ietf.org/html/rfc1123

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IDN's support UNICODE... which means that the browser will translate 'punycode' (characters that you mention) into something that displays in multiple languages. This is not the correct answer, but thank you. –  makerofthings7 Nov 16 '10 at 2:53
    
When searching for a domain name on godaddy, it tells me "Invalid character in domain. Only letters, numbers or hyphens are allowed." –  erimar77 Nov 16 '10 at 2:56
    
Yes, but I'm talking about an IDN. An IDN can be registered with godaddy once translated via punycode. This technology allows for unicode (non ASCII chars) to be used with traditional DNS. Google IDN, Punycode, etc, for more information. –  makerofthings7 Nov 16 '10 at 2:58
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It looks like it's defined per TLD, as an example: nunames.nu/Local-Language.cfm –  erimar77 Nov 16 '10 at 3:18

RFC 1035 is still the rule of the land when it comes to this. There are newer RFCs that explain how to encode unicode characters into so called LDH (lowercase, digits, hyphen) encoding. RFC 3492 describes punycode and 4690 summarizes the IDN landscape as a whole.

But to answer your question, only english alphabet letters, the digits from 0-9 and the hyphen character are allowed. Many DNS implementations also allow other characters such as the underscore "_".

Hopefully this helped, Rik

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