In message <b3ba5e37553642e28149093cdee78...@ahsnbw1>, "Al Stu" writes:
>
> Yes, the response to an MX query, that is the subject here. And a CNAME is
> in fact permitted and specified by the RFC's to be accepted as the response
> to an MX lookup.
No one is saying a CNAME is not permitted in response to a MX
query.
>
> "If the response does not contain an error response, and does not contain
> aliases"
> See there, alias is permitted. You just keep proving the my case.
We are saying that when you lookup the address of the mail
exchanger that you shouldn't get a CNAME record. MX ->
CNAME is not permitted. Others have quoted similar text
from more recent RFC's.
RFC 974
Note that the algorithm to delete irrelevant RRs breaks if LOCAL has
a alias and the alias is listed in the MX records for REMOTE. (E.g.
REMOTE has an MX of ALIAS, where ALIAS has a CNAME of LOCAL). This
can be avoided if aliases are never used in the data section of MX
RRs.
> I am not taking it out of context. It is very explicitly stated. And the
> context is that of locating the target/remote host by first submitting an MX
> query, then submitting an A query of the MX query result.
The text you quote is ONLY talking about the MX query.
There is no "then submitting an A query of the MX query
result" at this point in the RFC.
> The MX query
> result is permitted to be and alias, which in turn when submitted for an A
> query results in both the A and CNAME being returned. Thus meeting the SMTP
> RFC requirements.
> ----- Original Message -----
> From: "Mark Andrews" <mark_andr...@isc.org>
> To: "Al Stu" <al_...@verizon.net>
> Cc: <bind-users@lists.isc.org>
> Sent: Monday, January 26, 2009 8:41 PM
> Subject: Re: BIND 9.6 Flaw - CNAME vs. A Record in MX Records are NOT
> "Illegal"
>
>
> >
> > In message <3c802402a28c4b2390b088242a91f...@ahsnbw1>, "Al Stu" writes:
> >>
> >> RFC 974:
> >> "There is one other special case. If the response contains an answer
> >> which
> >> is a CNAME RR, it indicates that REMOTE is actually an alias for some
> >> other
> >> domain name. The query should be repeated with the canonical domain
> >> name."
> >
> > And that is talking about the response to a MX query. The section
> > from which you quote starts with:
> >
> > Issuing a Query
> >
> > The first step for the mailer at LOCAL is to issue a query for MX RRs
> > for REMOTE. It is strongly urged that this step be taken every time
> a mailer attempts to send the message. The hope is that changes in
> > the domain database will rapidly be used by mailers, and thus domain
> > administrators will be able to re-route in-transit messages for
> > defective hosts by simply changing their domain databases.
> >
> > and the paragraph after that which you quote is:
> >
> > If the response does not contain an error response, and does not
> > contain aliases, its answer section should be a (possibly zero
> > length) list of MX RRs for domain name REMOTE (or REMOTE's true
> > domain name if REMOTE was a alias). The next section describes how
> > this list is interpreted.
> >
> > So I would suggest that you stop taking text out of context.
> >
> > CNAME -> MX is legal
> > MX -> CNAME is illegal
> >
> > Mark
> >
> >> ----- Original Message -----
> >> From: "Scott Haneda" <talkli...@newgeo.com>
> >> To: "Al Stu" <al_...@verizon.net>
> >> Cc: <bind-users@lists.isc.org>
> >> Sent: Monday, January 26, 2009 8:09 PM
> >> Subject: Re: BIND 9.6 Flaw - CNAME vs. A Record in MX Records are NOT
> >> "Illegal"
> >>
> >>
> >> > On Jan 26, 2009, at 7:54 PM, Al Stu wrote:
> >> >
> >> >> If you refuse a CNAME then it is your SMTP server that is broken.
> >> >> The
> >> >> SMTP RFC's clearly state that SMTP servers are to accept and lookup a
> >> >> CNAME.
> >> >
> >> >
> >> > [RFC974] explicitly states that MX records shall not point to an alias
> >> > defined by a CNAME. That is what I was talking about, are you saying
> >> > this is not correct? As this is what I was under the impression for
> >> > quite some time.
> >> > --
> >> > Scott
> >> >
> >>
> >> _______________________________________________
> >> bind-users mailing list
> >> bind-users@lists.isc.org
> >> https://lists.isc.org/mailman/listinfo/bind-users
> > --
> > Mark Andrews, ISC
> > 1 Seymour St., Dundas Valley, NSW 2117, Australia
> > PHONE: +61 2 9871 4742 INTERNET: mark_andr...@isc.org
>
> _______________________________________________
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> bind-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/bind-users
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: mark_andr...@isc.org
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