RFC 973 (rfc973) - Page 2 of 10
Domain system changes and observations
Alternative Format: Original Text Document
RFC 973 January 1986
Domain System Changes and Observations
CLASS changes
Class 2, originally reserved for CSNET, is obsolete. Class 3 has
been assigned for use by CHAOS.
CNAME usage
The specification allows CNAME RRs to exist with other RRs at the
same node. This creates difficulties since the other RRs stored
with the CNAME at the alias might not agree with the RRs stored at
the primary name.
If a node has a CNAME RR, it should have no other RRs.
* semantics
The use of * to represent a single label wildcard, along with the
possibility of multiple * labels, led to difficult server
implementations and complicated search algorithms. There were
also questions regarding whether a * based specification could
refer to names that were not contained in the zone which had the *
specification.
While we might want the "inheritability" for some cases, it leads
to implementation difficulties. The first of these is that
whenever we can't find a RR in a particular zone, we have to
search all parent zones to look for a suitable * result.
(Alternatively we could develop some automatic method for insuring
consistency or insist on careful duplication of inherited data.)
We also must deal with conflicts, i.e. what if a subdomain doesn't
want to inherit defaults.
Given these difficulties, the solution is to insist that
delegation of authority cancels the * defaults. This is quite
simple to implement; all you need to do is to check for delegation
before looking for * RRs.
A second difficulty is the restriction that * match a single
label. Thus if a name server is looking for RRs for the name
A.B.C.D.E.F, it must check for *.B.C.D.E.F, *.*.C.D.E.F,
*.*.*.D.E.F, etc. This check must also be careful of zone
boundaries and multiplies the effort to handle a query.
The solution adopted is to allow a single * label in the leftmost
part of a name stored in a zone, and to allow this label to match
Mockapetris