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Asked: 2013-10-17 11:43:48 +0800 CST

linux initcwnd and initrwnd via /etc/sysctl.conf

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Folks, As we know, the 3.x kernels have higher TCP default connection values, such as initcwnd and initrwnd. For 2.x friends, is there a way to set these in /etc/sysctl.conf instead of the ip route way?

Instead of the following:

sudo ip route change default via 192.168.1.1 dev eth0  proto static initcwnd 10

Is there a way to set the same in /etc/sysctl.conf?

Thanks

linux

4 Answers

  1. Not quite answering the question but in December 2017 support for changing these values was added to systemd-networkd so you can now put this in /etc/systemd/network/*.network to make it persistent:

    [Route]
Gateway=_dhcp4
InitialCongestionWindow=10          # initcwnd
InitialAdvertisedReceiveWindow=10   # initrwnd

    The Gateway=_dhcp4 line is needed if you want the [Route] section to apply to the gateway supplied via DHCP. Otherwise add the Initial* lines to your existing [Route] section where you manually specify your gateway address.

    • 4

  2. By "via sysctl.conf" do you actually mean you want the settings to apply every boot?

    If so, you can write /sbin/ifup-local to run any commands as the last part of the interface start. The ifup script calls this with the interface name as a parameter.

    So your /sbin/ifup-local could contain:

    #!/bin/bash
if [[ "$1" == "eth0" ]]
then
  ip route change default via 192.168.1.1 dev eth0 proto static initcwnd 10
fi

    At least this works on RHEL/CentOS. I have not tried Deb/Ubu/others.

    • 2

  3. In case of CentOS 7 the script called in ifup is /sbin/ifup-pre-local . So i just made the script /sbin/ifup-pre-local :

    #!/bin/bash

defrt=`ip route | grep "^default" | head -1`
ip route change $defrt initcwnd 10

    And the initcwnd is set in all reboots and network restart.

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  4. On RHEL/CentOS/Oracle/Scientific Linux and other EL-based distro's:

    Easy, just don't specify GATEWAY= in your /etc/sysconfig/network-scripts/ifcfg-eth0 file. Then create a 2nd file called route-eth0 in the same place and write your gateway there:

      default via 192.168.0.1 initcwnd 10 initrwnd 10

    This method:

    • Keeps the network configuration in one place, where it should be to it is easy to find in the future and when servers are moved/upgrade.
    • Avoids creating unusual /sbin/ scripts that will be forgotten 10 years in the future
    • Doesn't depend on systemd
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