We just ordered a bunch of Hetzner EX40SSD servers with the minimal Debian install image that they provide and everything is just fine except that looking at tcpdumps for fine tuning the network from various locations the initcwnd param seems to be stuck at 6 no matter how we change it. By default Debian 3.2 kernels should have that setting to 10 so it's pretty strange. Is it possible that the NIC driver or a custom setting in the Hetzner Debian image is limiting this param? Even if we set it to 4, like the old kernel default, it doesn't work. Any ideas would be much appreciated!
Does anyone know if the NIC drivers provided by default by Debian have some kind on limitation. In a long thread in http://www.webhostingtalk.com/showthread.php?t=1200617&highlight=hetzner they talk about a page http://wiki.hetzner.de/index.php/Installation_des_r8168-Treibers/en where Hetzner states that the included Realtek r8168 driver is not working properly, but nowhere do they say that the initcwnd could be affected.
Tomorrow i will try to install a CentOs image and see if Debian is the problem...Last resort would be to install a custom debian image, but that is a pain in the ass!