If memory serves me right, Kaliaperumal, Rajesh wrote: > Hi all, > > > > Iperf version – iperf 3.1.3 > > > > My set up: iperf server (GCE) <=> Gateway VM (GCE) <=> IPsec server > (GCE) <=> WAN <=> Laptop with IPSec Client > > > > *My test:* > > Server – /iperf3 -s / > > Client – /iperf3 -c <server ip> -P 15 -R -w 768k/ > > Due to IPsec header, my Gateway VM modifies the MSS size of the > SYN-SYN/ACK message so that the TCP segments are not fragmented after > IPSec ESP encryption. > > > > *My Observation:* > > When I perform a downlink test by using the “-R” option at the iperf > client side, my throughput has a lot of variation and quickly drops to 1 > or 2 Mbps. In other words, the iPerf server reduces the rate at which it > pumps data. There are no packet drops on other VMs in my setup. > > > > I want to understand how iperf server determines the rate at which it > has to pump data?
With those parameters (and thank you for providing that information), the server basically just sends data as fast as it can on the 15 TCP connections you specified by the -P parameter. The speed at which it can send data is governed by the TCP congestion control and flow control algorithms. Of course those TCP connections will interact with each other, and any other network traffic along the path. If the system isn't behaving in a way that makes sense to you, might I suggest trying your experiment with just a single TCP connection? Also, what throughput were you expecting to get? Bruce.
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