forwarding to a child zone is different!!

[Brian Wellington]

On Mon, 23 Apr 2001, Kevin Darcy wrote:

> I disagree with the design decision that ISC has apparently made here. The
> ability to forward queries for a particular domain to some particular set of
> nameservers should not IMO depend on whether that domain happens to be delegated,
> or, worse yet, on whether the forwarding nameserver *knows* whether the domain is
> delegated or not because of pure happenstance it is also authoritative for an
> ancestor zone. Two machines sit side by side, each with a defined zone of type
> "forward" for foo.example.com, an undelegated domain; this forwarding works for
> one nameserver but not the other, because one of them happens to also be
> authoritative for some *other* zone (example.com). To me, this violates the
> Principle of Least Surprise. Forwarding is an *explicit* directive from the
> administrator, and often zones of "type forward" are created specifically
> *because* the zones are undelegated and that is the only way names in the domain
> can be resolved. The presence or absence of delegations for a domain, in turn,
> are often driven by local policy (e.g. security policy) which I don't think
> should be dictated by a DNS implementation.

This makes perfect sense, and follows the resolver algorithm specified in
RFC 1034.  Relevant parts quoted and annotated:

   2. Search the available zones for the zone which is the nearest
      ancestor to QNAME.  If such a zone is found, go to step 3,
      otherwise step 4.

If a child zone is not delegated properly, records under the child are in
the parent zone.  No amount of configuration changes the concept of
delegation, which is a property of the data.

   3. Start matching down, label by label, in the zone.  The
      matching process can terminate several ways:

         a. If the whole of QNAME is matched, we have found the
            node.

This doesn't happen, since the name doesn't exist.

         b. If a match would take us out of the authoritative data,
            we have a referral.  This happens when we encounter a
            node with NS RRs marking cuts along the bottom of a
            zone.

This would happen with a correctly configured delegation.

         c. If at some label, a match is impossible (i.e., the
            corresponding label does not exist), look to see if a
            the "*" label exists.

            If the "*" label does not exist, check whether the name
            we are looking for is the original QNAME in the query
            or a name we have followed due to a CNAME.  If the name
            is original, set an authoritative name error in the
            response and exit.  Otherwise just exit.

This is what happens.

> I also find it architecturally inconsistent to impose a new
> requirement that zones of type "forward" be delegated, if the same
> requirement is not imposed on zones of type "stub". The two mechanisms
> are logically similar, inasmuch as they are both ways to direct
> queries matching certain criteria to a specific set of nameservers,
> instead of following the normal delegation chain. That one works in
> the absence of zone delegation and the other does not is, as I said,
> inconsistent.

DNS doesn't have the concept of forward zones.  Forward zones are an
abomination of bind 8.  The point of them is domain-specific forwarding in
cases when the normal resolver algorithm is insufficient or will not work.
When delegation records are omitted and the data is part of an
authoritative zone, the resolver is never used.

> At the very least, since forwarding of undelegated domains/zones is
> something that worked in BIND 8 and by design (apparently) no longer
> works, this should be clearly documented in doc/misc/migration; the
> specific impact on forwarding is not something that can be clearly
> inferred from "No Information Leakage between Zones".

Maybe.  But don't forget that the whole reason this came up was a
configuration error.

Brian