On Tue, Apr 03, 2012 at 03:56:13PM +0100, Sam Jones wrote: > My senior tech and I have been having a squabble over PTR, > Hostnames and reverse mapping. > > If you have a client connect from 1.2.3.4 and perform a host name > lookup on that, so you get back host.example.com, would it impact > on mail if a forward query for host.example.com returned multiple > A records, say 1.2.3.4 & 5.6.7.8 alternating between the top of > the result sets in a round robin?
Multiple A records for a particular PTR value should not be a problem. The order in which those records are returned cannot be relied upon. If 192.0.2.22 connects to smtpd(8), and: 22.2.0.192.in-addr.arpa. PTR host.example.com. host.example.com. A 192.0.2.2 host.example.com. A 192.0.2.22 host.example.com. A 192.0.2.222 Postfix would log the connection as host.example.com[192.0.2.22]. "unknown[192.0.2.22]" is logged if: 1. 22.2.0.192.in-addr.arpa./PTR returns no value (including NXDOMAIN, SERVFAIL, and NOERROR) 2. Lookup of the 22.2.0.192.in-addr.arpa./PTR value does not return an A record with 192.0.2.22 as value. > I ask because we've seen an slightly odd pattern to some deferrals > with a host where this happens and wonder if they may be using: > > reject_unknown_client_hostname feature, which requires not only > that the address->name and name->address mappings exist, but > also that the two mappings reproduce the client IP address. See above. -- http://rob0.nodns4.us/ -- system administration and consulting Offlist GMX mail is seen only if "/dev/rob0" is in the Subject:
