[dnsext] errata on RFC1034 for recursive aliasing and name based diffrentiation

[Masataka Ohta <[e-mail]>]

While RFC1034 says:

   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.
   For example, the address to name RR for the above host
   should be:

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

   rather than pointing at USC-ISIC.ARPA.  Of course, by
   the robustness principle, domain software should not
   fail when presented with CNAME chains or loops; CNAME
   chains should be followed and CNAME loops signalled as
   an error.

"avoids extra indirections" is not a strong requirement
and virtually allowed with the wording of while "CNAME
loops signalled as an error" is a strong requirement.

Thus, while CNAME (and BNAME) chains should be discouraged,
it should be explicitly allowed to use CNAME as a target of
PTR, MX, SVR and so on which does not cause recursion loops,
which is useful for name based differentiation of a service
on a single host.

CNAME as a target of NS should also be discouraged, because
it may cause recursion loop to be resolved by glue, which
requires unnecessarily complex operations.


					Masataka Ohta