Forward timeout

Chris Buxton cbuxton at
Thu Mar 6 18:00:11 UTC 2008

As I recall, the behavior depends on BIND version of the server  
resending recursive queries to the forwarders.

BIND 9 < 9.3: Forwarders are tried in the order listed, for every  
query. So if the first forwarder goes down, queries are still sent  
there first, then fail over to the second after a short delay (1  

BIND 9 >= 9.3: Forwarders are ordered using the RTT algorithm. If a  
forwarder goes down, the following query may still go to it first,  
with a short delay followed by a query to the other. But after a small  
number of queries (I would think between 1 and 5), the name server  
will fixate on the other forwarder, periodically retrying the other to  
see if it's still down. When both servers are up, the RTT algorithm  
provides for efficient load balancing between them - if they are  
noticeably different in response time, the name server will fixate on  
the faster one.

None of this has anything to do with what user sent the original query.

Chris Buxton
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On Mar 5, 2008, at 9:16 PM, Jonathan Petersson wrote:

> Hi, I've a question in regards of forwarding;
> Example:
> ...
> forwarders {
> }
> ...
> Lets say that fails and the forward is redirected to
>, will this happen for each user or only once? And when
> it happens how long time does it take to fail over and is this option
> editable? When gets up again will the server fail back
> to it?
> Thanks
> /Jonathan

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