In /etc/sysctl.conf, add:

# disable packet forwarding
net.ipv4.ip_forward = 0
# enable source route verification
net.ipv4.conf.all.rp_filter = 1
# ignore broadcast pings
net.ipv4.icmp_echo_ignore_broadcasts = 1
# enable syn cookies
net.ipv4.tcp_syncookies = 1
# size of syn backlog
net.ipv4.tcp_max_syn_backlog = 512
# disable automatic defragmentation
# set max files
fs.file-max = 32768
# Enable IP spoofing protection, turn on Source Address Verification
net.ipv4.conf.all.rp_filter = 1
# Enable TCP SYN Cookie Protection
net.ipv4.tcp_syncookies = 1
# Enable ignoring ping request
net.ipv4.icmp_echo_ignore_all = 1

What does this do?
This sets a variety of code for the linux OS to use itself. It tells the system to ignore pings, icmp, enable SYN protection, disable network forwarding and more.

After doing this, you will need to restart your network (generally rebooting the server works fine).

In /etc/rc.local, add

for f in /proc/sys/net/ipv4/conf/*/rp_filter; do
echo 1 >
done
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
for f in /proc/sys/net/ipv4/conf/*/accept_source_route; do
echo 0 >
done
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all