On 10/24/2006 4:01 PM, John Rudd wrote: > Eric A. Hall wrote: >> Note that this is entirely legal, and even necessary: >> >> [ root# ] host 207.65.71.14 >> 14.71.65.207.in-addr.arpa is an alias for 14.in-addr.ntrg.com. >> 14.in-addr.ntrg.com is an alias for 14.in-addr.labs.ntrg.com. >> 14.in-addr.labs.ntrg.com domain name pointer bulldog.labs.ntrg.com. > > All of that's ok. The question is: > > is bulldog.labs.ntrg.com an A record, or a CNAME record? > > That's the thing I have been testing for (is it a CNAME). That's the > thing that RFC1912 doesn't like (the PTR record itself, not merely > in-addr.arpa aliases that eventually get to the PTR record, but the PTR > record itself, may not _refer_to_ a CNAME record, it must refer to an A > record)
There's nothing that prohibits the target domain name entry of a PTR from having a CNAME record. A PTR is just "a pointer to some other domain name". The target domain name can have whatever records the owner feels they need. It's probably something that should be discouraged, since additional processing would be needed to obtain a complete answer, but on its face it's not illegal (again RFC1912 is informational, is not authoritative, and has significant errors). You'd probably need a plugin to check for this, since you'd need to generate your own query for the RRs associated with the target domain name in order to get a definitive answer. I'm not really sure this would be reliable spam-sign. I can imagine some legitimate uses for this. -- Eric A. Hall http://www.ehsco.com/ Internet Core Protocols http://www.oreilly.com/catalog/coreprot/
