On 10/23/2006 10:50 PM, John Rudd wrote: > Eric A. Hall wrote: >> On 10/23/2006 7:01 PM, John Rudd wrote:
>>> a) does the hostname in the PTR record point to a CNAME instead of an A >>> record >> That's not illegal. It's pretty common too, since subnet delegation of >> in-addr space only works on /8, /16 and /24 subnets due to the way that >> octets are mapped to domain name labels in that hierarchy. > > RFC 1912 says "don't do that" :-) RFC1912 is informational non-authoritative. It has some big errors (ie, it says a label may not be all-numeric, which is wrong). > Though, honestly, I've yet to see it actually get triggered in my > mimedefang filter, so I don't mind losing it. Can you clarify what you are looking for here? 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. In that example, the entry for 14.71.65.207.in-addr.arpa. has a CNAME RR pointing to 14.in-addr.ntrg.com. (the entry has been delegated to my zone using a CNAME), which in turn aliases to 14.in-addr.labs.ntrg.com., which in turn has a PTR record that resolves to bulldog.labs.ntrg.com. A "PTR" record is just "a pointer to some other domain name" and only has semantic meaning when lookups are keyed to a name in the in-addr.arpa. hierarchy. -- Eric A. Hall http://www.ehsco.com/ Internet Core Protocols http://www.oreilly.com/catalog/coreprot/
