Subject: Re: Issue 27: Inappropriate use of NXRRSET RCODE

From: Bernard Aboba <[email-masked]>
Date: Wed, 19 Mar 2003 21:12:01 -0800 (PST)

A basic question about this issue. In going over the text changes, it
occurs to me that it may not be an either/or -- we may want to go to
LLMNR either for RCODE=3 *or* RCODE=0/ANCOUNT=0, or possible other
error cases, too. So I'd like to raise the general issue and see what
we come up with.

One scenario which concerned us was a home gateway that had a DNS Proxy
that holds only A RRs, dynamically registered via DHCPv4 (also implemented
on the gateway). If we assume the gateway doesn't support dynamic client
update or DHCPv6, then the question is how an IPv6-only host could resolve
names on the home network dynamically, using LLMNR.

So the question is what error one would receive from such a device on
sending it a unicast DNS query for a AAAA RR for a host that it has other
RRs for (A in this case). This would appear to be RCODE=0/ANCOUNT=0,
not RCODE=3 (Authoritative Name Error).

Another case is an ISP DNS server that doesn't do dynamic update, and
therefore doesn't contain any RRs for the home network hosts. Here a query
for an A/AAAA RR would return RCODE=3 (Authoritative Name Error), no? In
this case it also seems like LLMNR might be useful.

I'm curious if folks think there are other error codes that should trigger
LLMNR, too.

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From: [email-masked] (Andreas Gustafsson)
Date: Thu, 20 Mar 2003 11:32:50 -0800 (PST)

Bernard Aboba writes:
> on the gateway).

I am not familiar with this kind of "DNS proxy".  Is there a standards
document defining the functionality and behavior of such a device?

Perhaps the draft's use of the term "DNS proxy" without definition
should be raised as a separate Issue.

> not RCODE=3 (Authoritative Name Error).

Since I don't know what kind of "DNS proxy" the text is referring to
or how such a proxy is supposed to behave, I can't answer this
question.

> for an A/AAAA RR would return RCODE=3 (Authoritative Name Error), no?

If the DNS servers authoritative for the name used by the home network
host do not contain any RRs for it, they will return RCODE=3 (unless
the name is an empty nonterminal).  I would not use the term "an ISP
DNS server" since depending on the home network host's choice of name,
these servers may be completely unrelated to the home network's ISP.
-- 
Andreas Gustafsson, [email-masked]