> On Thu, 19 Nov 1998, Schreckenbach, Jan wrote:
>
> > What I don't understand is why underscores may be
> > valid in dns
> > (I can turn off the check in /etc/named.boot) but never in email
> > addresses.
>
> Mail addresses transferred over SMTP are defined in RFC 821, which does
> not allow underscores in mail domains. *That* is where the restriction
> arises. It is not a DNS restriction.
Er, RFC 1034 and RFC 1035 say:
2.3.1. Preferred name syntax
The DNS specifications attempt to be as general as possible in the rules
for constructing domain names. The idea is that the name of any
existing object can be expressed as a domain name with minimal changes.
However, when assigning a domain name for an object, the prudent user
will select a name which satisfies both the rules of the domain system
and any existing rules for the object, whether these rules are published
or implied by existing programs.
For example, when naming a mail domain, the user should satisfy both the
rules of this memo and those in RFC-822. When creating a new host name,
the old rules for HOSTS.TXT should be followed. This avoids problems
when old software is converted to use domain names.
The following syntax will result in fewer problems with many
applications that use domain names (e.g., mail, TELNET).
<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.
...thus severely warning off users using "funny" characters.
Later BIND versions are fascist about this.
M
--
Mark Murray
UUNET Internet Africa - Senior Network Engineer
Please visit
http://www.abuse.net - Help stamp out net.abuse
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