recursive-clients, what value ?

[Ladislav Vobr]

> default is off. Caching negative responses can GREATLY reduce the
> recursive-clients problem. If DNS for a high traffic domain is failing, and
> you're recursive clients are all hitting their timeouts waiting for a
> response when one won't be coming back then you'll end up again, seeing
> errors like the ones you saw.
it is by default in bind9 (3hours) and (10min for lame servers) only 
nxdomain, nxrrset are cached, servfail is not, time-outs are not, if 
*all* nameservers for high traffic domain are down, bind will keep 
flooding it sometimes with incredible rate depends purely on your 
clients, bind doesn't control it in any way,just amplify (by retries) 
you clients' flood and sends it to those "pure victim servers", same for 
servfail.
> 
>>Is there a way to monitor in real time the number of 
>>simultaneous clients ?
> You could probably get this from turning up debugging/query logging and
> parsing the data, but outside of that I'm not sure of any immediate way to
> get the number of simultaneous clients. I would suggest keeping track of
> your stats daily and looking at your long term trends, and be sure to look
> at your cache hit rate, it gives a good idea of what other things you can
> start tuning.
Richard, how can I plot cache hit rate? Do you mean rndc stats, there is 
only # of recursive requests.

Ladislav