On 4/7/08 at 9:54 AM -0700, Dave Crocker wrote:
John C Klensin wrote:
Someone would need to check with Craig Partridge...
A side discussion about history might be interesting, but I'll
suggest that it should not really be a factor for the current
discussion.
So, I want to disagree with Dave and wish to consider some history,
though Dave may have only been referring to the history leading up to
974. I think the history leading up to 2821 might be important:
1. 974 did *not* have an "A fallback" rule at all. 974 is quite clear
that the rule is, "If you can't find an MX, you should treat that as
if you *did* find an MX where the preference was 0 and the name in
the response was identical to the name queried. (That is, if you get
back no MXs for a.example.org, then it should be equivalent to
getting back a single MX of "a.example.org IN MX 0 a.example.org".)
If this rule were in effect today, you *would* connect to a mail
host's IPv6 address even if it had no MX records.
2. 2821 changed the rule and made explicit claims about looking for
fallback A records. The question is, was that intentional? Did DRUMS
intend to change the 974 rule in this regard, or was it trying to
explain what the 974 rule entailed by using examples? So far, I can
find nothing in the DRUMS archive to support the position that 2821
intentionally changed the 974 rules.
If 2821 had preserved the 974 MX rule, we would not be having this
discussion at all. The rule would be clear that the lack of the MX
got you an implicit MX, and then you'd look up A and AAAA records as
normal.
This entire argument reduces (for me) to answering this question: Did
2821 intend to preserve the 974 rule? If DRUMS did *not* intend to
change the 974 rule, then 2821's current text is an errant
interpretation of 974 and should be fixed back to the 974 rule. If
DRUMS *did* intend to change the rule to make it clear that 974 was
all about backwards-compatibility for hosts that didn't have MX
records, then there is a reasonable argument to be made for not doing
so for AAAA.
My current feeling is that 2821bis should clarify that it intended
the 974 rule. Yes, that gets us implicit MXs that point to AAAA
hosts. Such is life.
pr
--
Pete Resnick <http://www.qualcomm.com/~presnick/>
Qualcomm Incorporated - Direct phone: (858)651-4478, Fax: (858)651-1102