Linux Network tunning

 TCP tuning

Like most modern OSes, Linux now does a good job of auto-tuning the TCP buffers, but the  default maximum Linux TCP buffer sizes are too small. The following settings are recommended:

# increase TCP max buffer size setable using setsockopt()
# 16 MB with a few parallel streams is recommended for most 10G paths
# 32 MB might be needed for some very long end-to-end 10G or 40G paths
net.core.rmem_max = 16777216 
net.core.wmem_max = 16777216 
# increase Linux autotuning TCP buffer limits 
# min, default, and max number of bytes to use
# (only change the 3rd value, and make it 16 MB or more)
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
# recommended to increase this for 10G NICS
net.core.netdev_max_backlog = 30000
# these should be the default, but just to be sure
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 1

Note: you should leave net.tcp_mem alone. The defaults are fine.

Linux supports pluggable congestion control algorithms . To get a list of congestion control algorithms that are available in your kernel (kernal  2.6.20+), run:

sysctl net.ipv4.tcp_available_congestion_control

If cubic and/or htcp are not listed try the following, as most distributions include them as loadable kernel modules:

/sbin/modprobe tcp_htcp
/sbin/modprobe tcp_cubic