This is queryperf, a DNS server query performance testing tool. It is primarily intended for measuring the performance of authoritative DNS servers, but it has also been used for measuring caching server performance. This document describes the use of queryperf for authoritative server performance testing. NOTE: This version of queryperf has been modified by Nominum. It implements a slow-start algorithm which lessens the risk of network buffer overflows, particularly when testing recursive servers with high values for the -q option.