Maintained by: NLnet Labs

[Unbound-users] No answers from unbound occasionally

Joe Abley
Fri Jun 5 15:43:11 CEST 2009


On 4-Jun-2009, at 09:10, W.C.A. Wijngaards wrote:

> Attila Nagy wrote:
>> Hello,
>> I've made a capture and according to that, it was about 150 ms  
>> between
>> unbound's query and the response. I think it's pretty normal for
>> nameservers on the other side of the globe.
>
> Yes, however unbound keeps a rtt profile for each server.  So if the
> server has a very fast RTT then unbound will consider 150msec to be  
> very
> late (for that server), and retries before that time is up.

This suggests to me that for large, anycast-distributed servers there  
is an opportunity for unbound to give up to early whenever services  
are moved between far-distant anycast nodes.

What is the actual algorithm?

For example, if the RTT to an anycast server suddenly changes from  
reliably <20ms to something substantially higher, what is the  
threshold RTT at which we can expect unbound to stop being able to get  
answers?


Joe