Avoid Becoming an Unwitting Accomplice to a DDOS Attack: Tutorial on DOS Defense

"Perhaps the most basic way to combat DoS attacks is to overprovision your infrastructure. The good news is that overprovisioning your name servers isn't necessarily expensive; a capable name server can handle tens or even hundreds of thousands of queries per second. Not sure what your name servers' capacity is? You might use query tools such as dnsperf to test your name servers' performance -- preferably using a test platform similar to your production name servers in a lab rather than the production servers themselves:" InfoWorld

http://www.infoworld.com/t/security/the-ultimate-guide-preventing-dns-based-ddos-attacks-229790?page=0,0