iperf3 Tutorial: Network Bandwidth Is Not LLM Throughput
iperf3 measures data transferred between two test endpoints. It does not measure LLM tokens per second. Start with one forward TCP stream, preserve the receiver result and its units, and record the path and test conditions. A fast socket test can help diagnose a network path; it cannot establish RDMA, GPU collective or model-serving performance. Quick check before a test If the number looks eight times too large, check Mb/s versus MB/s first. If the client cannot connect, confirm the agreed server address, listener and narrow network access with its owner; do not disable the firewall. Run a short, rate-limited test only between endpoints you control and are authorized to load. Documentation checked October 25, 2026, Korea time. The network commands below were not executed : this Windows PC did not have iperf3 on PATH, and no remote test endpoints were approved. The Python parser was actually executed on a hand-written synthetic fixture using CPython 3.14.3. No network, GPU, NCCL o...