[Unbound-users] unbound closes receive socket => udp probes

Phil Mayers p.mayers at imperial.ac.uk
Mon Jul 8 15:03:49 UTC 2013

On 08/07/13 15:25, W.C.A. Wijngaards wrote:

>> I also think it would be good to alleviate this issue. It's polite
>> to the network and other hosts to properly receive reply packets to
>> your own requests, even if you no longer need them.
> The packets have timed out.  We do not expect them any longer.  A
> retry is probably sent over another port number (randomised) and thus
> uses a different socket.
> I do not know how to do what you ask - keep the port open for a reply
> that arrives later than expected, in a way that is good for
> performance and on resources.

Fair enough; if it's not possible in any sensible way, then it's not 

FWIW I do acknowledge the issues you raise; it is entirely possible 
there is no nice solution, other than what's already being done.

AFAIK there's no "/dev/null" for UDP sockets, though maybe you could 
emulate one by setting the SO_RCVBUF as small as possible and dropping 
it from the select/poll/epoll loop, with a close queued for some future 
time. But that'll probably still consume kernel resources. Whether this 
is a significant concern, I couldn't say - presumably you only have to 
"slow close" sockets that didn't receive a reply, which should be in a 

It could be more complicated than it's worth.

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