multiple PTR results

On Mon, Nov 17, 2003 at 10:19:04AM -0600, Dustin Trammell wrote:
| 
| However, if by not utilizing the feature we also make the assumption
| that a PTR will have a single record, then we will be ignoring the RFC.
| I don't see any way to ignore that PTRs may have multiple records and
| comply with the RFC concurrently.  I suggest we comply with the RFC and
| check for multiple PTR records per address.
| 

I have no problem with multiple PTRs.  The latest phrasing is:

5.4 'ptr'

   This mechanism tests if the <sending-host>'s name is within a
   particular domain.
   
        PTR = 'ptr' [ ':' domain-spec ]

   First <sending-host>'s name is looked up using this procedure:
   perform a PTR lookup against the <sending-host>'s IP.  For each
   record returned, validate the host name by looking up its IP address.
   If the <sending-host>'s IP is among the returned IP addresses, then
   that host name is validated.

   Check all validated hosts to see if they end in the <target-name>
   domain.  If any do, this mechanism matches.  If no validated hostname
   can be found, or if none of the validated hostnames end in the
   <target-name, this mechanism fails.

   This mechanism matches if the <target-name> is a parent node of the
   <sending-host>, or if the <target-name> and the <sending-host> are
   the same.  For example: "mail.example.com" is within the domain
   "example.com", but "mail.bad-example.com" is not.  If the
   <target-name> is hostname, a match results.

Here is some perl pseudocode.

  my ($sending_host, $target_name) = (some_ip, domain_spec);

  my @validated_host_names = ();

  foreach my $ptr_host_name (ptr_lookup($sending_host)) {
    foreach my $ip (a_lookup($ptr_host_name)) {
      push @validated_host_names, $ptr_host_name if $ip eq $sending_host;
    }
  }

  return "match" if grep { $_ eq $target_name or /\.$target_name$/ } 
@validated_host_names;

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