/etc/sysctl.conf

net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_syncookies = 1
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216

sysctlのすべての項目と値を表示

# sysctl -a

sysctlの項目を指定して表示

# sysctl -q net.ipv4.tcp_window_scaling

rebootしないで有効化

# sysctl -p /etc/sysctl.conf

項目を指定して有効化 (rebootで元に戻る)

# sysctl -w net.ipv4.tcp_window_scaling=1

Reference