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  1. #1
    Master Untangler
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    Nov 2009
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    Default Receive Window Scaling (rwin)

    Not an Untangle question, I realize, but someone here can probably answer the question off the top of his or her head.

    I'm using the default "free" installation:

    Build: 7.4.1~svn20100830r27350release7.4-1lenny

    with autoupdating turned on.

    For some reason, something insists on turning receive window scaling off. I've tried various approaches as detailed here:

    http://www.speedguide.net/articles/linux-tweaking-121

    with mixed results. For instance, at the moment /etc/sysctl.conf contains the line:

    net.ipv4.tcp_window_scaling = 1

    which IS correctly applied when sysctl -p is run from the command line. However, something, somewhere, at some mystery time, always goes and turns window scaling back OFF. If you execute sysctl -p again, it's back on until the mystery event once again turns it off. According to the Speedguide article, these parameters are applied at boot, which I have proven to be accurate. However, after a while, I discover that it's off again after a period of operation.

    Anyone have any ideas how to turn it on permanently and/or why the sysctl.conf setting is being overridden?

    And, before someone asks, window scaling really does make a visible difference on the speed of high-latency connections.

  2. #2
    Untangle Ninja jcoehoorn's Avatar
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    Default

    Untangle protects it's config files. If you want to alter one, you need to go to Config -> Networking -> Advanced -> Overrides and make sure your file is included in the list.

    Note that this is not recommended, as it can break updates. A better alternative is to add a cron job to apply your settings.
    Five time Microsoft ASP.Net MVP managing a Lenovo RD330 / E5-2420 / 16GB with Untangle 15.1.0 to protect 500Mbits for ~450 residential college students and associated staff and faculty

  3. #3
    Master Untangler
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    Nov 2009
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    Default

    Ah. Thank you. That's a useful piece of information. When you refer to Untangle's files, though, would that extend to these network configuration files that aren't part of the Untangle package and have nothing directly to do with Untangle operation?

    I'm not so sure that this is the answer though, because the sysctl.conf file is writeable already and retains the changes made to it. The problem seems to be that something comes along at (so far) unpredictable times and applies network configuration changes that conflict with sysctl.conf. IMO, this kind of behavior shouldn't happen as it breaks the intended operation of the OS. Furthermore, there's not a single good reason I can think of why Untangle should want to disable window scaling. Throughput really is better from high-latency sites when it's enabled.

    I thought about a cron job to reset it, but that just seems so ugly.... My sense of tidiness would prefer to find out what's really going on and fix it there.

  4. #4
    Untangle Ninja jcoehoorn's Avatar
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    Default

    Untangle encompasses the entire linux distribution. They are free to change any file during updates, up to and including the kernel. This is way cron job is the preferred method for this - a job that you add is unlikely to be replaced during an update.
    Five time Microsoft ASP.Net MVP managing a Lenovo RD330 / E5-2420 / 16GB with Untangle 15.1.0 to protect 500Mbits for ~450 residential college students and associated staff and faculty

  5. #5
    Untangle Ninja sky-knight's Avatar
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    Default

    The UVM will on start and stop make an inspection of an ever changing and unspecified list of system files. sysctl.conf is on that list. You must override it, a cron job won't work in this case. If my memory is correct sysctl.conf is over written every time you make a change or request a view of config -> networking. There is also an automatic check that can reset the system file every 15min.

    Use the override, disable automatic upgrades, and disable the override when you upgrade. These kinds of hacks are a bit dirty, but they can be made safely as long as you take responsibility for them.
    Rob Sandling, BS:SWE, MCP
    NexgenAppliances.com
    Phone: 866-794-8879 x201
    Email: support@nexgenappliances.com

  6. #6
    Master Untangler
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    Default

    It's like I always say: Nothing is ever simple.

    Far as I can see, sysctl.conf retains the "....window_scaling = 1" indefinitely. At least it has been unchanged for the last three weeks, so we can probably say indefinitely. The actual state of window_scaling seems to reset to 0 on one or two occasions each week.

    BTW, I tried setting "30 * * * * /sbin/sysctl -p" in root's crontab and it's ignored. cron is running, crontab buys the entry without complaint, but it no workee.

    Something in this system is intent on keeping window scaling off.

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