Re: Port-forwarding Perfomance

[Andy Furniss <andy.furniss@dsl.pipex.com>]

Rudi Starcevic wrote:
> Hi,
> 
> 
> I'm still seeing slow performance with my port-forwarding but
> have found something interesting that may be problematic.
> 
> Just to re-cap:
> 
> I have one Linux 66.283.12.21 box and one Windows box 192.168.0.10
> I can download a file of the linux box at around 140K/s
> That very same file download on the Windows machine is around 15K/s 
> using DNAT and Masq/Forwarding.
> 
> However we can upload to the Windows box at 140k/s.
> 
> So it is only slow, 15K/s, when the data is coming from Windows then 
> through the Linux Iptables Masq/Forwarding Firewall.
> 
> I contacted an earlier Admin for the Windows machine and was informed 
> the TCP window size has been manually increased.
> 
> Could this affect Forwarding in Iptables ?
> 
> The default maximum TCP window size in Win2000 is 17520 bytes (12 
> segments).
> The current value is set at 131400.

Max window size is 64k without scaling - so I assume they have turned 
scaling on aswell - there have been problems with scaling, one of the 
linux kernel releases set it to 7 which confused buggy peers. AIUI they 
turned it back down to workaround.

You could tcpdump so you can can see what's going on.


> 
> 90% of the traffic being port-forwarded are Digital video files.
> These range in size from 2MB to 200MB.
> 
> So I assume with large files like these Windows would opt for it's 
> largest TCP window size.
> 
> I guess the next step is to lower these to their default values and see 
> if it affect bandwidth.
> 
> Your thoughts on that would be much appreciated.
> 
> Thanks.
> Regards,
> Rudi
> 
> 
> 
>