address-to-names

[Hongbo Shi]

Dear all, 

 I have thought about the PTR RR for long time.
 I still not quite sure why PTR RR is based on the "one IP one domain"
 consideration in [RFC1034]. 
 I hope somebody can answer this question for me. 

[RFC1034]
cname & aliases:
 "Most of these systems have a notion that one of the equivalent set of
  names is the canonical or primary name and all others are aliases."

PTR:
 "Domain names in RRs which point at another name should always point at
 the primary name and not the alias.  This avoids extra indirections in
 accessing information."

 Furthermore a lot of persons regard the domain name used in the A record 
as a cname. Is it correct? Is it misunderstanding? Is there some new RFCs
already permitted the consideration?

 And then based on the cosideration above, if the following A records exist, 

 A.ISI.EDU    IN   A    10.0.0.52
 B.ISI.EDU    IN   A    10.0.0.52
 C.ISI.EDU    IN   A    10.0.0.52

 of course "address-to-names" should exist.

 52.0.0.10.IN-ADDR.ARPA  IN      PTR     A.ISI.EDU
 52.0.0.10.IN-ADDR.ARPA  IN      PTR     B.ISI.EDU
 52.0.0.10.IN-ADDR.ARPA  IN      PTR     C.ISI.EDU

%[RFC1034] didn't describe that a name used in A record should be regarded 
 as a cname, as far as I know.

Best Regards

Hongbo Shi