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Re: What is the history of 2821 and implict MX?

2008-04-11 06:05:55

--On Friday, 11 April, 2008 00:47 -0400 "Robert A. Rosenberg"
<hal9001(_at_)panix(_dot_)com> wrote:

At 19:12 -0400 on 04/09/2008, John C Klensin wrote about Re:
What is the history of 2821 and implict MX?:

--On Wednesday, 09 April, 2008 17:21 -0400 "Robert A.
Rosenberg" <hal9001(_at_)panix(_dot_)com> wrote:

 At 14:29 -0500 on 04/08/2008, Pete Resnick wrote about Re:
 What is the history of 2821 and implict MX?:

 The MX rule of 974 is perfectly reasonable to apply to IPv4
 and IPv6.

 RFC 974 also requires the use of a WKS record to verify that
 the IPN address has a MTA running on it.

Please read RFC 1123 (section numbers mentioned in an earlier
note).  Use of WKS was explicitly deprecated; the MX rule was
not changed.


I am aware of RFC 1123 and you are quoting me (and referencing
RFC 1123) out of context since that statement was immediately
followed by "Since we do not use WKS records for this purpose
..." thus indicating (but not explicitly mentioning RFC 1123
as the reason) I was aware of the WKS deprecation (although it
might have been better to have said "no longer" not "do not").


I think you misunderstood the comment I was trying to make.
That was probably my fault for not being more explicit, for
which I apologize.   I was responding more to "...for this
purpose" than the specifics of using WKS or not.   

More specifically...

We have tried variations on "look over here (e.g., in the DNS)
to see, definitively, if something is available over there
(e.g., some service)" several times, with similar results.
Those results closely parallel discoveries in [other] areas of
computer science (see e.g., Ed Codd's original paper on
relational database models). If one has two different, but
intimately related, pieces of information that are stored in
different places and often maintained by different people in
different roles, things _will_ get out of synch and to bad
effect.  Often it doesn't even require different people -- it is
just too hard to keep track when things need to be updated in
different types of systems.

One may need to read a bit between the lines of 1123, but the
comments surrounding the deprecation of WKS should be
interpreted at least as much as "didn't work this time either,
let's not try it again" as "well, that didn't work, better luck
next time". 

Like it or not, there is a big difference between using the DNS
to advertise the availability or location of a service and
believing that the absence of information in the DNS is a
definitive indication that the service doesn't exist at that
node.  It will be that way until and unless we redesign the
network architecture to treat the DNS as part of TCP or IP such
that, e.g., the act of turning on a listener for a particular
service is the act that creates corresponding records in the
DNS.     That is the message in the failure of WKS as a
definitive service-availability indicator and what I was trying
to point you to when I pointed you to 1123.