Trying to understand why does iperf to analyse the bandwidth of certain servers leads to large overflow (high bandwidth/transfer)

Hi all,

I'm currently doing some bandwidth analysis of public iperf servers. I've noticed that I've been getting a large overflow from certain servers (So, the transfer is 1,000,000,000 bits, and the bandwidth is say 1,000,000,000 mbytes, as an example). I can't find definitive answers regarding this, but apparently if a server is using or not using the "iperf -s" flag, then this explains this anomaly. (Several iperf servers show "normal" results).

I guess, I understand that -s is basically telling how many connections a server can have (based off the documentation: -s, --server : iPerf2 can handle multiple client requests. iPerf3 will only allow one iperf connection at a time.).

I'm using iperf 2, so I can't really figure out how does the servers using/not using -s lead to overflow. Can someone help me regarding the theory behind this?