iperf3 + virtualbox machines

Test Complete. Summary Results:
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-60.00  sec  4.76 GBytes   682 Mbits/sec  83625             sender
[  4]   0.00-60.00  sec  4.76 GBytes   682 Mbits/sec                  receiver
[  6]   0.00-60.00  sec  4.49 GBytes   642 Mbits/sec  85820             sender
[  6]   0.00-60.00  sec  4.48 GBytes   642 Mbits/sec                  receiver
[  8]   0.00-60.00  sec  3.79 GBytes   542 Mbits/sec  78816             sender
[  8]   0.00-60.00  sec  3.78 GBytes   542 Mbits/sec                  receiver
[ 10]   0.00-60.00  sec  3.07 GBytes   440 Mbits/sec  69753             sender
[ 10]   0.00-60.00  sec  3.07 GBytes   440 Mbits/sec                  receiver
[ 12]   0.00-60.00  sec  2.65 GBytes   380 Mbits/sec  65566             sender
[ 12]   0.00-60.00  sec  2.65 GBytes   379 Mbits/sec                  receiver
[ 14]   0.00-60.00  sec  2.49 GBytes   356 Mbits/sec  63142             sender
[ 14]   0.00-60.00  sec  2.48 GBytes   356 Mbits/sec                  receiver
[ 16]   0.00-60.00  sec  2.34 GBytes   335 Mbits/sec  60530             sender
[ 16]   0.00-60.00  sec  2.34 GBytes   335 Mbits/sec                  receiver
[ 18]   0.00-60.00  sec  2.07 GBytes   297 Mbits/sec  52428             sender
[ 18]   0.00-60.00  sec  2.07 GBytes   297 Mbits/sec                  receiver
[SUM]   0.00-60.00  sec  25.7 GBytes  3.67 Gbits/sec  559680             sender
[SUM]   0.00-60.00  sec  25.6 GBytes  3.67 Gbits/sec                  receiver
CPU Utilization: local/sender 15.5% (0.3%u/15.3%s), remote/receiver 10.4% (0.1%u/10.2%s)

so this is the data from between two virtual box machines on my mac...

client:
iperf3 -c 192.168.56.101 -i 1 -t 60 -V -p 80 -P 8

server:
iperf3 -s -p 80

i don't understand why those retry numbers are so high...

---

## Vagrant file:
Vagrant.configure("2") do |config|
  config.vm.define "web" do |web|
    web.vm.box = "ubuntu/xenial64"
    web.vm.hostname = 'web'
    web.vm.box_url = "ubuntu/xenial64"

    web.vm.network :private_network, ip: "192.168.56.101"

    web.vm.provider :virtualbox do |v|
      v.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
      v.customize ["modifyvm", :id, "--memory", 512]
      v.customize ["modifyvm", :id, "--name", "web"]
    end
  end

  config.vm.define "db" do |db|
    db.vm.box = "ubuntu/xenial64"
    db.vm.hostname = 'db'
    db.vm.box_url = "ubuntu/xenial64"

    db.vm.network :private_network, ip: "192.168.56.102"

    db.vm.provider :virtualbox do |v|
      v.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
      v.customize ["modifyvm", :id, "--memory", 512]
      v.customize ["modifyvm", :id, "--name", "db"]
    end
  end
end


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sudo apt-get update && sudo apt-get install -y iperf3