Allow CloudFlare only

cloudflare.sh

# Source:
# https://www.cloudflare.com/ips
# https://support.cloudflare.com/hc/en-us/articles/200169166-How-do-I-whitelist-CloudFlare-s-IP-addresses-in-iptables-

# Backup/Restore
# iptables-save > savedrules.txt
# cat savedrules.txt
# iptables-restore < savedrules.txt 

for i in `curl https://www.cloudflare.com/ips-v4`; do iptables -I INPUT -p tcp -m multiport --dports http,https -s $i -j ACCEPT; done
for i in `curl https://www.cloudflare.com/ips-v6`; do ip6tables -I INPUT -p tcp -m multiport --dports http,https -s $i -j ACCEPT; done

# Avoid racking up billing/attacks
# WARNING: If you get attacked and CloudFlare drops you, your site(s) will be unreachable. 
iptables -A INPUT -p tcp -m multiport --dports http,https -j DROP
ip6tables -A INPUT -p tcp -m multiport --dports http,https -j DROP


# chmod +x cloudflare.sh
# sh cloudflare.sh || bash cloudflare.sh