forwarding with bind8.3.7

Kevin Darcy kcd at
Tue Jan 13 23:41:18 UTC 2004

Matus UHLAR - fantomas wrote:

>I have 3 dns servers doing DNS lookups and for speeding up some requests
>I'd like to set up forwarding of queries between them.
>I've read the documentstion (not the sources) and I see that I can set up
>option "forward first". However I am not sure if it won't have negative 
>impact on speed of requests that are not in cache of any server.
Yes, it can have a negative impact, depending on your server and/or 
network capacity. In some topologies, however, the inter-nameserver 
latency may be so low, and the Internet connectivity of the "central" 
server so much faster than that of the other servers, that it may be 
faster to forward that way than to attempt iterative resolution, even in 
the "worst case scenario" where nobody has anything cached. Generally 
speaking, though, forwarding is going to slow down your "worst case 
scenarios", so you have to ask yourself at the outset whether that is 
worth a possible modest increase in your average query turnaround time. 
I tend to avoid forwarding whenever possible: in the tests I've done it 
doesn't seem to net much performance increase, if any, and introduces 
more points of a failure and a more complex/convoluted architecture to 
troubleshoot when something goes wrong. There are situations, however, 
where I can't avoid it, but those are "forward only" 
network-connectivity situations.

>I'd like to know - what's the timeout before DNS Server sends the requests
>to outside after they were sent to peers without reply.
>Is it possible to tune the timeout somehow?
Sorry, I don't know the exact value of the timeout, but in a quick test 
I just did, it appears to be about a 1-second failover (relatively-late 
version of BIND 9). Non-tunable, as far as I know...

                                                - Kevin

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