Don't request read receipts when you post to this mailing list please? Thanks loads. . wrote:
Hi,I'm trying to find out if it is allowed to have several hostnames being returned from inverse DNS queries (example see below). RFC 1034 and RFC 1035 don't seem to answer that question.Example:bulma:~# dig -x 193.158.67.67 ; <<>> DiG 9.2.1 <<>> -x 193.158.67.67 ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14939 ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;67.67.158.193.in-addr.arpa. IN PTR ;; ANSWER SECTION: 67.67.158.193.in-addr.arpa. 77637 IN PTR bulma.condor-werke.com. 67.67.158.193.in-addr.arpa. 77637 IN PTR vegeta.condor-werke.com.67.67.158.193.in-addr.arpa. 77637 IN PTR fairlane.condor-werke.com.;; AUTHORITY SECTION: 67.158.193.in-addr.arpa. 77637 IN NS pns.dtag.de. 67.158.193.in-addr.arpa. 77637 IN NS secondary007.dtag.net. ;; Query time: 1 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Fri Jan 27 17:09:21 2006 ;; MSG SIZE rcvd: 184 bulma:~# dig PTR 67.67.158.193.in-addr.arpa ; <<>> DiG 9.2.1 <<>> PTR 67.67.158.193.in-addr.arpa ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24431 ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;67.67.158.193.in-addr.arpa. IN PTR ;; ANSWER SECTION: 67.67.158.193.in-addr.arpa. 77635 IN PTR vegeta.condor-werke.com.67.67.158.193.in-addr.arpa. 77635 IN PTR fairlane.condor-werke.com.67.67.158.193.in-addr.arpa. 77635 IN PTR bulma.condor-werke.com. ;; AUTHORITY SECTION: 67.158.193.in-addr.arpa. 77635 IN NS pns.dtag.de. 67.158.193.in-addr.arpa. 77635 IN NS secondary007.dtag.net. ;; Query time: 1 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Fri Jan 27 17:09:23 2006 ;; MSG SIZE rcvd: 184 bulma:~#As you can see, the inverse lookup does return three hostnames that share the same IP address (because they are behind a gateway). All the hostnames returned are primary hostnames from the hosts' point of view. But one could argue that from the point of view of those who do the inverse lookup, only one of the names returned can possibly be a primary host name or that at last it cannot be (easily) decided which one is a primary host name or which one should be used from there on for the purposes the request was made for.It could also be argued that an inverse lookup _should_ always return an unambigous result, in the same way in that CNAME records are supposed to always point to a primary hostname rather than to other CNAME records.But RFC 1035 explicity states that answers to inverse lookups may yield inconsistent data because "the IN-ADDR.ARPA special domain and the normal domain for a particular host or gateway will be in different zones". That applies especially to hosts having multiple IP addresses (like the gateways).Yet I've found no example of an IP address resolving into multiple host names when making an inverse lockup on that address.Is there any RFC or other documentation consindering that case? Where would be a definitive place to ask such a question?As a matter of fact, the above PTR records oficially exist. Maybe that can be taken as a hint that it is allowed to have them? :)GH