No, you're confusing hostnames and domain names. Read Ed Lewis' draft, https://tools.ietf.org/html/draft-lewis-domain-names-02
On Thu, Apr 7, 2016 at 10:37 PM, Adrien de Croy <adr...@qbik.com> wrote: > Hi all > > I guess you're all aware of the issue of what constitutes a valid domain > name, what characters are valid in labels etc. So forgive me for what must > be me re-raising an ancient maybe long-thought-put-to-rest issue... > > but there's a serious problem out there. > > RFC1034 secion 3.5 which is almost copied in RFC1035 section 2.3.1, both > labelled "preferred name syntax" clearly define > > > > <domain> ::= <subdomain> | " " > > <subdomain> ::= <label> | <subdomain> "." <label> > > <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ] > > <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> > > <let-dig-hyp> ::= <let-dig> | "-" > > <let-dig> ::= <letter> | <digit> > > <letter> ::= any one of the 52 alphabetic characters A through Z in > upper case and a through z in lower case > > <digit> ::= any one of the ten digits 0 through 9 > > Note that while upper and lower case letters are allowed in domain > names, no significance is attached to the case. That is, two names with > the same spelling but different case are to be treated as if identical. > > The labels must follow the rules for ARPANET host names. They must > start with a letter, end with a letter or digit, and have as interior > characters only letters, digits, and hyphen. There are also some > restrictions on the length. Labels must be 63 characters or less. > > > which allows DNS labels (not just host names) to contain alphanumeric and > hyphen only. There doesn't seem to be a MUST level requirement to use > this, but there doesn't seem to be any specification elsewhere in the > documents either. > > > RFC2818 on the other hand says > > > > The DNS itself places only one restriction on the particular labels > that can be used to identify resource records. That one restriction > relates to the length of the label and the full name. The length of > any one label is limited to between 1 and 63 octets. A full domain > name is limited to 255 octets (including the separators). The zero > length full name is defined as representing the root of the DNS tree, > and is typically written and displayed as ".". Those restrictions > aside, any binary string whatever can be used as the label of any > resource record. Similarly, any binary string can serve as the value > of any record that includes a domain name as some or all of its value > (SOA, NS, MX, PTR, CNAME, and any others that may be added). > > > > So how did we get from alphanumeric+hyphen to "any binary"? > > If we truly allow "any binary" why the need for special ascii-compatible > encodings for IDN? > > Later RFCs (the ones I checked) seem to corroborate RFC2818, but I'm > pretty sure the last time I tried to register a domain I couldn't enter any > special chars. So there's a (probably mixed) de facto standard in use > anyway. > > Plus the countless pages on various answer sites about "what is a valid > DNS name" which state alphanumeric+hyphen, and seem to gloss over the > underscore used for SRV records. > > Is this just a mess that it's been decided we can't really adequately fix? > > Thanks > > Adrien > > _______________________________________________ > DNSOP mailing list > DNSOP@ietf.org > https://www.ietf.org/mailman/listinfo/dnsop > >
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