Hi Paul,
Which version of named are you running? You've likely run into an issue
that we've seen before - basically, as you have surmised, your server
has to retry each query and never gets a response regarding edns (so it
can't "remember"). Let me know which version you are running and I'll
get back to you regarding the availability of a "fix."
You can mitigate this issue by using "edns-udp-size 512" in the
appropriate server clause or use "edns no" to turn off edns altogether.
Thanks,
-Scott
On 06/24/2011 01:22 PM, Paul Wouters wrote:
Hi,
I'm investigating an outage that happened on a bind server. It was
configured as a caching resolving name server. It was forwarding for
one specific zone. This zone had two nameservers/forwarders of which one
at some point was unreachable due to a cable cut. The other nameserver
turned out to be dropping any requests with the DO bit set.
What seems to have happened is:
1 the bind nameserver would send 3 queries 1s apart with ENDS0+DO bit,
which were
dropped.
2 bind sends out a query without the DO bit, it gets a response with
TTL=0
3 a burst of queued up queries for that exact query gets rushed
through for 1s
(prob not more then max-clients-per-query though, which was set at 100)
4 goto 1
This not only caused resolving failures for the forwarding data, but
within the hour
caused the entire server to collapse under load. The number of clients
asking
for this data was higher then the max-clients-per-query setting.
My questions:
1 Is this problem happening because EDNS failure is not remembered for
forwarders?
2 Is this problem happening because EDNS failure is forgotten once
there is no more
data cached that used the specified nameserver?
3 Does max-clients-per-query apply to forward zone queries too, or is
this ignored?
4 Can this behaviour be changed via a configuration option so we can
remember this EDNS
failure so that we're not unable to anser queries for 3 out of 4
seconds?
Paul
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