Options Used within iptables Commands https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/3/html/Reference_Guide/s1-iptables-options.html
Minimal Iptables Configuration – Developer Should Know http://developer-should-know.tumblr.com/post/128018906292/minimal-iptables-configuration
How to troubleshoot DNS with dig and nslookup https://www.a2hosting.com/kb/getting-started-guide/internet-and-networking/troubleshooting-dns-with-dig-and-nslookup
How to access your account using SSH keys https://www.a2hosting.com/kb/getting-started-guide/accessing-your-account/using-ssh-keys#Mac-OS-X-and-Linux-operating-systems