failed forwarder timeout

Iain Pople ipople at
Wed Sep 20 07:55:42 UTC 2006


We are running bind 9.2.4 on RHEL4 as a caching only name server. We 
have 2 forwarders listed. I have found that if one of the forwarders is 
unreachable, then BIND still tries to query the first forwarder for 
every query before failing over to the second listed forwarder. This 
introduces a 2 second delay for every query.

I assume that this behaviour is because BIND 9 ignores the RTT value for 

There is an interesting yet dangerous side effect of the 2 second delay. 
If you have a large number of recursive queries to your server, then the 
delay causes them to rapidly bank up, which means that you can exceed 
your limit for recursive-clients. At this point BIND stops answering 
queries and is essentially failing.

- Has this behaviour been changed in more recent versions of BIND?
- Is the 2 second timeout configurable?
- Are there any strategies for dealing with this, or do busy servers 
generally turn off forwarding.

thanks, Iain.

Iain Pople
Systems Interface Technical Lead
University of Melbourne

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