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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" :
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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.
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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.
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