a) Increase TCP window size
b) Enable TCP SYN cookies. This prevents SYN floods on incoming connections
c) Increase TCP send and receive buffers
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
All these are edits to /etc/sysctl.conf which is a configuration file to configure/edit kernel parameters at runtime.
#sysctl -p /etc/sysctl.conf
to enable your changes, and
to see what else has been configured.