Resolver optimization of auth selection - Truth or Myth?

Barry Margolin barmar at
Mon Feb 8 19:26:29 UTC 2016

In article <mailman.189.1454958428.73610.bind-users at>,
 "Darcy Kevin (FCA)" <kevin.darcy at> wrote:

>                 If you take a look at sections 4.1 & 4.2 - they seem to say  
>                 BIND 9.8 gets it a little backwards and starts to prefer 
>                 higher latency servers?

It doesn't say it prefers high-latency servers. It occasionally tries 
the high-latency servers, because it decays the low-latency SRTT.

The purpose of this is to prevent permanently blackholing a server when 
it's temporarily slow. So every now and then it will switch to the 
high-latency server. If it's still high latency, it will lose preference 
again, and it will go back to the low-latency servers. But if it has 
gotten better, it will continue to be used.

Network distance is not the only reason for high latency, sometimes it 
can be because of heavy load on the server, or a congested network link, 
or other temporary conditions.

Barry Margolin
Arlington, MA

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