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I've tried changing the tcp's window size by modifying net.ipv4.tcp_wmem and net.ipv4.tcp_rmem values, however the changes which I make have no effect on actual window size which I can check using a wireshark.

I tried to do that on 2 different kernels (3.2.69 and 2.6.38) with no effect at all.

I've even tried to change the min/default numbers to an absurd level and disable window_scaling but still no effect - window size remains exactly the same. What do I do wrong?

-- EDIT -- I've updated the kernel to 3.14.57 and the TCP's window size doubled without doing any other change. It looks like this value is controlled somewhere else and kernel actually ignores net.ipv4.tcp_wmem / net.ipv4.tcp_rmem values.

  • How / where did you modify the values? – gf_ Dec 5 '15 at 13:01
  • And don't forget that the actual window size which is used gets negotiated between the client and the server to something they both support, an adjusted send window on the server requires adjusting the client receive window too. (and vice-versa) – HBruijn Dec 5 '15 at 13:08
  • @gf_: I used sysctl -w to update the values – rfire Dec 5 '15 at 14:13
  • @HBruijn: I'm aware of that but that's not the case. I've updated the kernel on the test machine to 3.14.57 and... The tcp's window size doubled without doing any other change. It looks like it's controlled by something else and kernel actually ignores net.ipv4.tcp_rmem/net.ipv4.tcp_wmem values. – rfire Dec 5 '15 at 14:16

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