TCP/IP advanced: Ports

You have a basic understanding of TCP/IP ( IP-address, subnet-mask, Gateway, DNS, DHCP,....),
but now it is time to look at an advanced issue, which has a serious impact on network security,
especially when using TCP/IP to connect to the Internet: Ports.
Let's start by looking in the Control-Panel at "Internet Options" :

Connection a single PC to the Internet
is easy, it becomes more complex when
you connect a network of multiple PCs
via a single connection to the Internet.
In such cases, you will need a Proxy,
and you need to configure on the
tab: Connections the "Lan Settings",
where you need to define PORT information.

TCP/IP is a complex protocol, offering multiple services (especially on the Internet), like:
- HTTP (=Web-Browsing)
- FTP (File Transfer Protocol)
- e-mail
- file sharing
For each of these services, a kind of "sub-dialect" of TCP/IP is used, call : PORT.

Each PORT has a number assigned to it, here a list of the most common PORTS:

PORT:	Service:	Purpose / usage :
21	FTP	FTP: File Transfer Protocol, often used to download software programs and / or updates from the Internet
23	Telnet	Telnet allows to work with a command-line interface on a System, originally developed for UNIX (so it includes now LINUX systems ! ), but also available on some NT-systems
25	SMTP	used to send e-mail messages to an Internet Mail Server
80	HTTP	used to retrieve WWW pages
110	POP3	used to receive e-mail messages from an Internet Mail Server
139	NETBIOS	used for Microsoft networking to handle File-Sharing
443	HTTPS	used to retrieve SECURE WWW pages

To protect your system against attacks from the Internet using one of these TCP/IP ports, you
should install a Personal Firewall.