On Fri, 2006-01-27 at 18:44 +0100, . 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. > >
the RFC's dont explicitly deny the use of multiple PTR records. but all books i have read, bot on dns and on bind discourage it's usage. The returned hostnames from the PTR records are returned in a random order. so it's dificult to predict witch is returned. and i don't know of any software that checks anything but the first returned result. with regards Ronny Aasen -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
