On Tue, 28 Jun 2011, Cathy Almond wrote:
BIND does take notice of this and it's something we're looking at to
make better in future releases. But at the moment it's not foolproof
and its effectiveness is dependent on circumstances.
There is short term caching of learned 'we don't support EDNS' servers.
But reaching the point of being able to process and cache them is
dependent on how many servers we're dealing with for a zone that we're
querying and also how far down the 'trail' of handling a client query we
happen to be. If the client query times out before BIND has finished
trying and timing out, then it doesn't get to cache what it was in the
process of learning.
This problem was the reverse. Thousands of clients were asking it, and the
backlog only increased over time because 3 out of 4 seconds the forwarder
was unavailable due to DO packets getting dropped.
Paul
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