failed forwarder timeout
ipople at unimelb.edu.au
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.
Systems Interface Technical Lead
University of Melbourne
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