5장. Tuning TCP connections for high throughput

Procedure

1. Optional: Display the maximum network speed of the network interface controller (NIC) on both the server and client:

   # ethtool enp1s0 | grep "Speed"
      Speed: 100000Mb/s

2. On the server:

   1. Temporarily open the default iperf3 TCP port 5201 in the firewalld service:

      # firewall-cmd --add-port=5201/tcp

   2. Start iperf3 in server mode:

      # iperf3 --server

      The service now is waiting for incoming client connections.

3. On the client:

   1. Start measuring the throughput:

      # iperf3 --time 60 --zerocopy --client 192.0.2.1

      • --time <seconds>: Defines the time in seconds when the client stops the transmission.

        Set this parameter to a value that you expect to work and increase it in later measurements. If the client ends packets at a faster rate than the devices on the transmit path or the server can process, packets can be dropped.

      • --zerocopy: Enables a zero copy method instead of using the write() system call. You require this option only if you want to simulate a zero-copy-capable application or to reach 40 Gbps and more on a single stream.
      • --client <server>: Enables the client mode and sets the IP address or name of the server that runs the iperf3 server.

4. Wait until iperf3 completes the test. Both the server and the client display statistics every second and a summary at the end. For example, the following is a summary displayed on a client:

   [ ID] Interval         Transfer    Bitrate         Retr
   [  5] 0.00-60.00  sec  101 GBytes   14.4 Gbits/sec   0   sender
   [  5] 0.00-60.04  sec  101 GBytes   14.4 Gbits/sec       receiver

   In this example, the average bitrate was 14.4 Gbps.

5. On the server:

   1. Press Ctrl+C to stop the iperf3 server.

   2. Close the TCP port 5201 in firewalld:

      # firewall-cmd --remove-port=5201/tcp