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List: courier-users
Subject: Re: [courier-users] RFC 1035
From: Matthias Wimmer <m () tthias ! eu>
Date: 2012-06-28 23:12:02
Message-ID: 4FECE4C2.10805 () tthias ! eu
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Hi Jan,
okay I think you are right, that 192.0.2.15. shouldn't be considered a
valid domain.
But your EBNF has been releaxed by RFC 1123, section 2.1:
The syntax of a legal Internet host name was specified in RFC-952
[DNS:4]. One aspect of host name syntax is hereby changed: the
restriction on the first character is relaxed to allow either a
letter or a digit. Host software MUST support this more liberal
syntax.
[...]
If a dotted-decimal number can be entered without such
identifying delimiters, then a full syntactic check must be
made, because a segment of a host domain name is now allowed
to begin with a digit and could legally be entirely numeric
(see Section 6.1.2.4). However, a valid host name can never
have the dotted-decimal form #.#.#.#, since at least the
highest-level component label will be alphabetic.
There are many examples, where digit-only labels are used in the DNS.
Some of them even defined by other RFCs:
411.org
1und1.com
2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.4.2.2.0.a.0.0.8.f.4.0.1.0.a.2.ip6.arpa
9.35.198.88.in-addr.arpa
0.7.7.7.0.0.7.7.0.0.7.9.4.e164.arpa
And in any case "192.0.2.15." when set in the MX record is still a
domain (and not an IP), but you convinced me, that this domain is invalid.
Defined by section 3.3.9 the "EXCHANGE" contains a domain (and not an
IPv4 address which is encoded binary in DNS).
Regards,
Matthias
BTW: Even the last sentence I have quoted is now further relaxed by the
non-ASCII TLDs we have.
Am 28.06.12 23:01, schrieb Jan Ingvoldstad:
> On Thu, Jun 28, 2012 at 6:24 PM, Matthias Wimmer <m@tthias.eu
> <mailto:m@tthias.eu>> wrote:
> >
> >
> > Well technically I'd say that the (invalid) MX *is* pointing to a domain
> > name, but that domain name does not exist.
> >
> > There is no way an IP address can be in an MX record. There can just be
> > some (non-existent) domain, that *looks* *like* an IP address with an
> > additional point at the end.
> >
> > For example: AFAIK "192.0.2.10." is a perfectly valid domain name, it is
> > just not present in the DNS.
> >
>
> RFC 1035:
>
> <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>
>
> --
> Jan
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<pre wrap="">Hi Jan,
okay I think you are right, that 192.0.2.15. shouldn't be considered a
valid domain.
But your EBNF has been releaxed by RFC 1123, section 2.1:
The syntax of a legal Internet host name was specified in RFC-952
[DNS:4]. One aspect of host name syntax is hereby changed: the
restriction on the first character is relaxed to allow either a
letter or a digit. Host software MUST support this more liberal
syntax.
[...]
If a dotted-decimal number can be entered without such
identifying delimiters, then a full syntactic check must be
made, because a segment of a host domain name is now allowed
to begin with a digit and could legally be entirely numeric
(see Section 6.1.2.4). However, a valid host name can never
have the dotted-decimal form #.#.#.#, since at least the
highest-level component label will be alphabetic.
There are many examples, where digit-only labels are used in the DNS.
Some of them even defined by other RFCs:
411.org
1und1.com
2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.4.2.2.0.a.0.0.8.f.4.0.1.0.a.2.ip6.arpa
9.35.198.88.in-addr.arpa
0.7.7.7.0.0.7.7.0.0.7.9.4.e164.arpa
And in any case "192.0.2.15." when set in the MX record is still a
domain (and not an IP), but you convinced me, that this domain is invalid.
Defined by section 3.3.9 the "EXCHANGE" contains a domain (and not an
IPv4 address which is encoded binary in DNS).
Regards,
Matthias
BTW: Even the last sentence I have quoted is now further relaxed by the
non-ASCII TLDs we have.
</pre>
<div class="moz-cite-prefix">Am 28.06.12 23:01, schrieb Jan
Ingvoldstad:<br>
</div>
<blockquote
cite="mid:CAEffzkzcCQcfEpY0akLyGtXPPzZKS9-_MLTOYrEdpeCLDChMog@mail.gmail.com"
type="cite">On Thu, Jun 28, 2012 at 6:24 PM, Matthias Wimmer <<a
moz-do-not-send="true" href="mailto:m@tthias.eu">m@tthias.eu</a>>
wrote:<br>
><br>
><br>
> Well technically I'd say that the (invalid) MX *is* pointing
to a domain<br>
> name, but that domain name does not exist.<br>
><br>
> There is no way an IP address can be in an MX record. There
can just be<br>
> some (non-existent) domain, that *looks* *like* an IP address
with an<br>
> additional point at the end.<br>
><br>
> For example: AFAIK "192.0.2.10." is a perfectly valid domain
name, it is<br>
> just not present in the DNS.<br>
>
<div><br>
</div>
<div>RFC 1035:<br>
<br>
<domain> ::= <subdomain> | " "<br>
<br>
<subdomain> ::= <label> | <subdomain> "."
<label><br>
<br>
<label> ::= <letter> [ [ <ldh-str> ]
<let-dig> ]<br>
<br>
<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp>
<ldh-str><br>
<br>
<let-dig-hyp> ::= <let-dig> | "-"<br>
<br>
<let-dig> ::= <letter> | <digit> <br>
<br>
--<br>
Jan</div>
</blockquote>
<br>
<br>
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