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What characters are you allowed to use in a subdomain?
Example: for someSub.example.com the someSub portion.
I know you can use letters, numbers, and hyphens, but what about other characters? Can _ (underscore) be used?
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Keyword: What characters can a domain name contain? A domain name can only contain the letters A-Z, the digits 0-9 and hyphen (-), in addition to one punctuation (.)
A subdomain is a domain that is part of a larger domain. Each label may contain from 1 to 63 octets. The full domain name may not exceed a total length of 253 ASCII characters in its textual representation.
The use of underscore characters is a little confusing. Underscore characters are not permitted in domain names in accordance with RFC 1035, which only allows letters, digits and hyphens. As such, you cannot register a domain name with an underscore character.
4 Answers. Show activity on this post. Hyphens in subdomains are just as acceptable as hyphens in domain names.
Letters (except stressed à), Numbers 0-9 and Hyphen.
http://en.wikipedia.org/wiki/Domain_name excerpt: Valid characters that can be used in a domain name are:
a-z 0-9 - but not as a starting or ending character . as a separator for the textual portions of a domain name From https://www.rfc-editor.org/rfc/rfc1035
Various objects and parameters in the DNS have size limits. They are listed below. Some could be easily changed, others are more fundamental.
labels 63 octets or less names 255 octets or less TTL positive values of a signed 32 bit number. UDP messages 512 octets or less According to this page, some top level domains now allow localized characters (not just a-z).
-------------------------------------------------------------------------------- | Top Level Domain | Allowed Characters | -------------------------------------------------------------------------------- | .no | áàäčçđéèêŋńñóòôöšŧüžæøå | | .se | àáäåæçèéêëìíîïðñòóôöøùúüýþćčđěłńŋřśšţŧźžǎǐǒǔǥǧǩǯəʒ, plus Hebrew | .dk | äåæéöøü | .is | áéýúíóþæöð | .it | àâäèéêëìîïòôöùûüæœçÿ | .fr | àáâãäåæçèéêëìíîïñòóôõöùúûüýÿœ | .nu | àáâäåāæçèéêëēìíîïīðñŋòóôõöøōùúûüūýþÿ | .be | àáâãäåæçèéêëìíîïðñòóôõöøùúûüýþÿœ | .de | àáâãäåāăąæçćĉċčďđèéêëēĕėęěŋðĝğġģĥħìíîïĩīĭįıĵķĸĺļľł | | ñńņňòóôõöøōŏőœŕŗřśŝşšţťŧþùúûüũūŭůűųŵýÿŷźżž | .as | Same as .de | .com | Same as .de, plus Greek, Cyrillic, Chinese, Korean, etc. | .net | Same as .de, plus Greek, Cyrillic, Chinese, Korean, etc. | .org | áäåāąæćčéēėęģíīįķļłñńņðóöøōőŗśšúüūűųýźżžþ plus Cyrillic and Korean | .info | áäåāąæćčéēėęģíīįķļłńņðóöøōőŗśšúüūűųýźżžþ plus Korean | .biz | àáäåæéêíðñòóôöøúüýþ -------------------------------------------------------------------------------- So, looks like we need to go back to the drawing board on that regex.
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