https://ritazh.com/setup-your-own-l2tp-vpn-server-with-raspberry-pi-170d3d4df04c
https://www.raspberrypi.org/forums/viewtopic.php?t=31541
https://www.raspberrypi.org/forums/viewtopic.php?t=195174
https://superuser.com/questions/556427/is-there-top-for-disk-usage
http://www.microhowto.info/howto/configure_apache_as_a_reverse_proxy.html
https://www.digitalocean.com/community/tutorials/how-to-use-apache-as-a-reverse-proxy-with-mod_proxy-on-ubuntu-16-04
https://www.digitalocean.com/community/questions/apache-proxypass-and-reverseproxy-to-a-ssl-https-configured-domain
https://www.digitalocean.com/community/tutorials/how-to-use-apache-http-server-as-reverse-proxy-using-mod_proxy-extension
https://frillip.com/using-your-raspberry-pi-3-as-a-wifi-access-point-with-hostapd/
https://www.vivaolinux.com.br/dica/Configuracao-do-ddclient-no-Debian
Letting DHCP requests through iptables
https://www.frozentux.net/iptables-tutorial/chunkyhtml/x6316.html
http://blog.mxard.com/persistent-iptables-on-raspberry-pi-raspbian
http://www.noveldevices.co.uk/rp-dhcp-server
http://www.braindisconnect.com/wiki/index.php?title=Linux_DHCP_Server
https://documentation.cpanel.net/display/CKB/Guide+to+DNS+Cluster+Configurations
https://documentation.cpanel.net/display/68Docs/Installation+Guide+-+cPanel+DNSONLY+Installation