Re: Download speed and TCPIP window sizing


On Thu, 31 May 2007 22:06:39 +0800, Pang <freebsd@xxxxxxx> wrote:
Recently, I have leased a rack in Asianetcom and some bandwidth.
However, the speed for my curcuit is substantially slower than my
provider's company site.
[...]
*This server is using FreeBSD 6.2 patch 4 with Apache in the port tree.
The kernel is custom built but I haven't made any modification in sysctl

I have asked many techs in Asianetcom and they blamed on TCPIP window
sizing.

I used to have the same problem with my FreeBSD dedicated servers in the U.S. when I was living in South America with a latency of ~200 ms. Given identical hardware and connectivity, I could max out my download speed when downloading from a server running Linux, but would get no more than 100-150 KB/s when downloading from an otherwise identical FreeBSD box.

The solution was to increase the size of the TCP send window on the FreeBSD server to about 128 KB--the default of 32 KB turned out to be way too small.

# sysctl net.inet.tcp.sendspace=131072

After modifying this value, you need to restart any processes (e.g. Apache) that you want to take advantage of the change.

Hope it helps.

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    ... The kernel is custom built but I haven't made any modification in sysctl ... I have asked many techs in Asianetcom and they blamed on TCPIP window ... The solution was to increase the size of the TCP send window on the FreeBSD server to about 128 KB--the default of 32 KB turned out to be way too small. ...
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