Threshold of DNS servers to handle queries

[Ryan Bernard]

Hi do you guys know if it is possible to determine the threshold of DNS servers to handle queries? Is there any thing that we can do to forecast when the servers is reaching its limit?

Thanks~

[Steven Schweda]

Define "threshold".

Send it a query, and see if it's too slow to
respond?

[Bill Thorsteinson]

Recent bind notices indicated that with the new randomized port patches you may run into problems when the load hits 10000 queries per second.

[Ryan Bernard]

What I am concern if the servers' threshold is met, there will be reduction in performance? Any limit that we should look for before we can determine that threshold is met?

[Bill Thorsteinson]

DNS like all servers will slow down as the load increases. If you are monitoring responses with a tool like Nagios you can monitor response time.

Areas to watch for impacts of over load are the network UDP request queues. If these fill up, then packets will be dropped, and the request will be redone to another server. This will delay resolution. If you are worried, watch your UDP network stats.

On a caching server, memory can be an issue, although these days it is much less likely.
Any reasonably sized server should be sufficient.

I am not aware of CPU load ever having been a problem.