Place the following code in /etc/rc.local or /etc/boot.local, depending on your distribution (it needs to be reapplied at startup). The settings below assume you're using eth0 for your internet connection, the TCP/IP parameters should be self-explanatory:
ifconfig eth0 mtu 1500
echo 256960 >> /proc/sys/net/core/rmem_default
echo 256960 >> /proc/sys/net/core/rmem_max
echo 0 >> /proc/sys/net/ipv4/tcp_timestamps
echo 1 >> /proc/sys/net/ipv4/tcp_sack
echo 1 >> /proc/sys/net/ipv4/tcp_window_scaling
Change the RWIN/MTU values above as desired, depending on your internet connection and maximum throughput/latency. There are other parameters you can change from the default if you're confident in what you're doing - just find the correct syntax of the values in /proc/sys/net... and add a line in the above code analogous to the others.
To revert to the default parameters, just comment or delete the above code from /etc/rc.local and restart.
For additional information see
Linux Tweaking.
