# cat /etc/network/options 
ip_forward=yes
spoofprotect=no
syncookies=no

# sysctl -p
net.ipv4.conf.default.forwarding = 1
net.ipv4.conf.default.proxy_arp = 0
net.ipv4.conf.all.rp_filter = 1
kernel.sysrq = 1
net.ipv4.conf.default.send_redirects = 1
net.ipv4.conf.all.send_redirects = 0
net.ipv4.tcp_max_orphans = 131072
net.ipv4.tcp_mem = 720896 865075 1038090
net.ipv4.ip_forward = 1