On Sat, Feb 20, 1999 at 09:32:54AM -0800, Greg Skinner wrote:
I am actually responding to Roeland's comment here...
> Roeland Meyer wrote:
> > Sure, but first you'll have to prove that there is a problem, Chicken
> > Little. Show me a failure mode that I can repeat.
There is no failure mode that you can repeat, because the failure
mode exists in the entire DNS, not in a particular node. Caching
behavior is a global property of DNS, not just a property of a
single running copy of bind. Your failure to comprehend this simple
fact is a fundamental error.
> > Point to code that shows
> > the architectural flaw. Yes, there is one small section, in the caching
> > code, that is slightly non-deterministic in certain conditions.
> > However, my
> > personal examination did not yield any failure modes in the code. testing
> > specifically, and generally, also did not reveal any flaws.
Your personal examination of the code is largely irrelevant. This
is a problem inherent in the global structure of DNS, not the bind
code.
Are you familiar with the smurf attack, where the attacker can cause
thousands of pings per second to flood into a particular address?
That's not a failure mode that is visible in the networking code that
replies to broadcast addresses, or something you would detect by looking
at the source for "ping"; it's a failure mode in the overall
system design. There are what?, 43,000,000 nodes in the DNS, and
they are all caching almost everything, so the vast majority of
requests never go through the roots.
It is well-known that a small change in caching characteristics can
sometimes cause a drastic change in performance -- it's a non-linear
response. One example of this phenomenon is how network performance
degrades precipitously past a certain threshold, when retries start
to clog the system. Another example is disk thrashing when the
working set for a code is significantly bigger than the page cache.
Note that DNS traffic is already a significant fraction of the
traffic on the backbones.
--
Kent Crispin, PAB Chair "Do good, and you'll be
[EMAIL PROTECTED] lonesome." -- Mark Twain
