Forward timeout

Chris Buxton cbuxton at menandmice.com
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  
second?).

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
Professional Services
Men & Mice
Address: Noatun 17, IS-105, Reykjavik, Iceland
Phone:   +354 412 1500
Email:   cbuxton at menandmice.com
www.menandmice.com

Men & Mice
We bring control and flexibility to network management

This e-mail and its attachments may contain confidential and  
privileged information only intended for the person or entity to which  
it is addressed. If the reader of this message is not the intended  
recipient, you are hereby notified that any retention, dissemination,  
distribution or copy of this e-mail is strictly prohibited. If you  
have received this e-mail in error, please notify us immediately by  
reply e-mail and immediately delete this message and all its attachment.



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

> Hi, I've a question in regards of forwarding;
>
> Example:
>
> ...
> forwarders {
>    123.123.123.123;
>    231.231.231.231;
> }
> ...
>
> Lets say that 123.123.123.123 fails and the forward is redirected to
> 231.231.231.231, 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 123.123.123.123 gets up again will the server fail back
> to it?
>
> Thanks
>
> /Jonathan
>



More information about the bind-users mailing list