005 Netstat-for-Windows
https://help.fasthosts.co.uk/app/answers/detail/a_id/1552/~/netstat-explained

005 Netstat-for-Linux
https://www.binarytides.com/linux-netstat-command-examples/

006 Nmap-Reference-Guide
https://nmap.org/book/man.html#man-description

006 Nmap-Tutorial
https://www.cyberciti.biz/security/nmap-command-examples-tutorials/

008 DROP-vs.REJECT
https://unix.stackexchange.com/questions/109459/is-it-better-to-set-j-reject-or-j-drop-in-iptables