Differences

This shows you the differences between two versions of the page.

--- mscom_network_start [2014/04/03 15:12]
beckmanf removed linux setup, moved to separate link
+++ mscom_network_start [2016/03/16 09:01] (current)
beckmanf [Setup of the Linux test platform / USB Stick] - removed student laptop
@@ Line 5: / Line 5: @@
 Details regarding tcp testing are here: [[http://www.linuxfoundation.org/collaborate/workgroups/networking/tcp_testing]].
-==== Setup of the Linux test platform / USB Stick ====
+==== Setup of the Linux test platform ====
-Network tests are done with a network of Ubuntu Linux computers which are connected via an ethernet switch. Students laptops will be part of the setup. If you have a native linux installation, you can use that directly. Follow the steps in [[mscom_linux_setup|Master COM Linux test setup / USB Stick]]. If have a laptop which does not have a native linux installation, then you can use a bootable USB Stick which we provide.
+Network tests are done with a network of Ubuntu Linux computers which are connected via an ethernet switch.
 ==== Laboratory expirements ====
   * [[mscom_lab1|Master COM Lab 1 - Ethernet Measurements]]
+  * [[mscom_lab2|Master COM Lab 2 - tftp Measurements]]
 ==== TCP Throughput test with iperf ====
@@ Line 124: / Line 123: @@
 ==== Adding tcpprobe traffic log ====
+The tcp_probe module can trace the state of a tcp connection.
+<code>
+sudo modprobe tcp_probe port=5001
+sudo chmod a+r /proc/net/tcpprobe
+</code>
+In order to store the log data in file test.log:
+<code>
+cat /proc/net/tcpprobe > test.log
+</code>
+tcp_probe only adds a log entry, when the contention window size changes. In order to have a log entry for every received packet
+<code>
+sudo modprobe tcp_probe port=5001 full=1
+</code>
+The Ubuntu 12.04 LTS is based on linux kernel 3.11. The tcp_probe kernel module source code can be viewed on the [[https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/tcp_probe.c?id=v3.11|linux kernel git server]].
+To unload the module:
+<code>
+sudo modprobe -r tcp_probe
+</code>
+The log file from tcp_probe contains lines with the log information
+<code>
+           2                    3                   4  5          6          7  8          9     10
+.768727538 192.168.178.33:51715 192.168.178.27:5001 32 0xe656e892 0xe6568e12 16 2147483647 42248 1
+: Time in seconds
+: Source IP:Port
+: Destination IP:Port
+: Packet length in bytes
+: snd_nxt: Sequence Number of the next packet to send
+: snd_una: Sequence Number of the first unacknowledged packet
+: snd_cwnd: Contention Window
+: ssthr: Slow Start Threshold (-1 => not known yet)
+: snd_wnd: Send Window size in Bytes
+: srtt: Averaged round trip time estimation
+</code>
+The data from the log file can be plotted with gnu plot
+<code>
+gnuplot
+gnuplot> plot "test.log" using 1:7 title "cwnd", "test.log" using 1:($8 > 20000000 ? 0 : $8) title "ssthr"
+</code>
+==== TCP configuration ====
+=== Local memory restrictions ===
+Set the maximum window sizes for tcp connections to 512000 Bytes.
+<code>
+sudo sh -c "echo 512000 > /proc/sys/net/core/wmem_max"
+sudo sh -c "echo 512000 > /proc/sys/net/core/wmem_default"
+sudo sh -c "echo 512000 > /proc/sys/net/core/rmem_max"
+sudo sh -c "echo 512000 > /proc/sys/net/core/rmem_default"
+sudo sh -c "echo 512000 512000 512000 > /proc/sys/net/ipv4/tcp_wmem"
+sudo sh -c "echo 512000 512000 512000 > /proc/sys/net/ipv4/tcp_rmem"
+</code>
+=== Initial TCP contention window size ===
+The following section shows how to change the initial contention window size to to 1 MSS.
+<code>
+fritz@ubuntu:~$ ip route show
+default via 192.168.178.1 dev eth0  proto static
+.254.0.0/16 dev eth0  scope link  metric 1000
+.168.178.0/24 dev eth0  proto kernel  scope link  src 192.168.178.33  metric 1
+fritz@ubuntu:~$ sudo ip route change default via 192.168.178.1 dev eth0 proto static initcwnd 1
+fritz@ubuntu:~$ ip route show
+default via 192.168.178.1 dev eth0  proto static  initcwnd 1
+.254.0.0/16 dev eth0  scope link  metric 1000
+.168.178.0/24 dev eth0  proto kernel  scope link  src 192.168.178.33  metric 1
+fritz@ubuntu:~$
+</code>
+=== TCP Congestion avoidance algorithm selection ===
+The linux kernel provides several algorithms for tcp congestion avoidance. The following code shows how to figure out the available algorithms (here cubic and reno) and set and control the setting. In this example the congestion avoidance algorithm is switched from "cubic" to "reno".
+<code>
+fritz$ cd /proc/sys/net/ipv4/
+fritz$ cat tcp_available_congestion_control
+cubic reno
+fritz$ cat tcp_congestion_control
+cubic
+fritz$ sudo sh -c "echo reno > tcp_congestion_control"
+fritz$ cat tcp_congestion_control
+reno
+</code>