Flowgrind is an advanced TCP traffic generator for testing and benchmarking Linux, FreeBSD, and Mac OS X TCP/IP stacks. In contrast to similar tools like iperf or netperf it features a distributed architecture, where throughput and other metrics are measured between arbitrary flowgrind server processes.

Flowgrind measures besides goodput (throughput), the application layer interarrival time (IAT) and round-trip time (RTT), blockcount and network transactions/s. Unlike most cross-platform testing tools, flowgrind can output some transport layer information, which are usually internal to the TCP/IP stack. For example, on Linux and FreeBSD this includes among others the kernel's estimation of the end-to-end RTT, the size of the TCP congestion window (CWND) and slow start threshold (SSTHRESH).

Flowgrind has a distributed architecture. It is split into two components: the flowgrind daemon and the flowgrind controller. Using the controller, flows between any two systems running the flowgrind daemon can be setup (third party tests). At regular intervals during the test the controller collects and displays the measured results from the daemons. It can run multiple flows at once with the same or different settings and individually schedule every one. Test and control connection can optionally be diverted to different interfaces.

The traffic generation itself is either bulk transfer, rate-limited, or sophisticated request/response tests. Flowgrind uses libpcap to automatically dump traffic for qualitative analysis.