Re: is this proper behavior?

[Rob Austein <sra+dnsop@hactrn.net>]

At Mon, 24 Jun 2002 17:40:05 -0400, Edward Lewis wrote:
> 
> (This is the question that led me to ask this on DNSOP.)  Is it 
> acceptable for a server to answer for some zones and not at all for 
> others?  Wouldn't this cause a problem for DNS implementations that 
> measure round trip times in order to select one server over another? 

Depends on the algorithm.  If the observed behavior were that the name
server repeatedly answers queries for different names at different
speeds (that is, if there were a repeatable pattern to the round trip
times), I'd agree that it was a measurement problem.  As you describe
it, though, it's a sampling problem (which data does one feed into the
RTT estimator?), which is a subtly different thing.   TCP, for
example, would not regard lack of response as any kind of sample at
all (that is, the connection would of course eventually time out, and
the RTO would back off, but the RTT estimate would not change -- see
RFC 1122 4.2.3.1 and follow the references to the SIGCOMM papers).

With all that said, the behavior you describe is questionable in light
of the robustness principle, so it's probably a bad thing unless
there's a very good reason for doing things that way.