How can I find bottlenecks using IPERF3?

Question

I've just started using IPERF and I'm rather confused about the results I'm getting. When IPERF reports bandwidth does it actually mean throughput as when repeating tests the values returned seem to change and I would have thought bandwidth would be static? I'm just testing on an artificial network without any other traffic at the moment.

How would I be able to use IPERF to find bottlenecks within my network? I thought I could use IPERF, check when the CWND drops, then look for the link/device that was likely to be causing this but this doesn't seem to work. The network has an artificial packet loss assigned to each link ranging from 0.1-5%.

Answer 1

iperf can help you generate flows of a certain bandwidth. You can then check if your network behaves as designed and examine your equipment for signs of problems: packet drops due to exceeding aggregate bandwidth, overrunning buffers, CPU overload, significant rates of checksum errors, and so on.

A simulated network might behave somewhat differently from a real one. The simulation is limited for real-time or high-frequency effects and the simulated individual device might not act exactly like the real thing. For instance, simulated bad links behave statistically and rather unlike a real-world problem.

Trying to understand the behavior based on the derived CWND parameter isn't easy. You should first run the simulation with an error-free link and check how congestion control works without interference.

With random link errors, each frame drop is sensed as congestion, reducing the CWND - in conjunction with real congestion this can behave pretty eratically.