On Thu, Nov 01, 2001 at 02:54:11AM -0500, Greg A. Woods wrote:
|
| Unless you're prepared to fix some other RFCs then you can't get rid of
| it. Remember this from 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 addressed exactly this issue in my original argument. The
complex phrasing of the above paragraph tends to
short-circuit normal critical evaluation and produces a sort
of cognitive kneejerk reaction.

The RFC974 scenario above lost its strength when sendmail's
Cw was introduced. Under postfix, mydestination solves the
same problem.

permit_mx_backup sees right through MX->CNAME->A chains and
does the same thing as if it were an MX->A chain.

| Besides that there are lots of instances where code would have to be
| updated (I've got at least two instances myself!). Not everything does
| lookups in such a way that further CNAMEs will be resolved!

Could you provide more details please?

I understand that the resolver library will, when given an
alias, automatically perform the relevant A lookup and
return the IP address of the canonical name.

% perl -MNet::DNS -le 'my $res = new Net::DNS::Resolver; for
($res->search("rfc1912cname.mengwong.com")->answer) { next
unless $_->type eq "A"; print $_->type . " " . $_->address
}'
A 208.210.125.21

If the resolver instead returned only the CNAME record and
expected the calling application to further resolve the
canonical name to its IP address, then there would be a
problem, because we can't expect all applications to do
their own CNAME resolution.

But the resolver library makes CNAMEs transparent to the
calling application, so I don't see the objection.

| Why do you want to make things more complex anyway? Why not K.I.S.S.
| and just leave MX RRs as simple pointers to hostnames, the way they were
| designed to be?

I don't want to make things more complex. In practice I
don't do MX->CNAME at all. What I am doing is playing
scientist in search of The Truth; I submit that avoiding
MX->CNAME is the postmaster's version of not stepping on
cracks or walking under ladders.

-
To unsubscribe, send mail to majordomopostfix.org with content
(not subject): unsubscribe postfix-users

• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]