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Glossary
IP network
Port
Port forwarding
FRITZ!Box Fon WLAN 7570 vDSL
A network in which data exchange takes place on the basis
of the Internet Protocol is called an IP network.
So that a single network connection on a connection can be
used by multiple applications to exchange data with re-
mote sites at the same time, a computer administers what
are known as ports for the IP-based protocols TCP and UDP.
Ports substantiate the point of access for the data packets
delivered via the IP Internet protocol. While the IP address
determines the destination computer quite generally, the
port addresses the communication interface provided by
an application for a certain communication procedure.
The Internet protocol allots 16 bits for the specification of
the port number. Thus a total of 65,535 different port num-
bers can be specified. Ports up to port number 1,024 are re-
served for special system applications and typical Internet
applications. These include, for instance, the port numbers
21 for FTP (File Transfer Protocol), 25 for SMTP (Simple Mail
Transfer Protocol), 53 for DNS (Domain Name Service) and
80 for HTTP (Hypertext Transfer Protocol).
Ports are primarily of interest to users for their role in pro-
tecting an Internet connection from external attacks. Most
firewalls offer the possibility of preventing data traffic on
certain ports. This means that certain port numbers can be
blocked to prevent data from being delivered to system ser-
vices. This is also a way of preventing any Trojans (mali-
cious applications opening backdoors on a computer) that
may have infected your computer from receiving data on
ports it created as means of accessing your computer for
potentially damaging activities. A firewall blocks most atyp-
ical port numbers not required for normal operation of an
application and offers specialized users the opportunity to
forward specified ports.
With port forwarding it is possible to specify ports that will
allow all incoming or outgoing data packets to pass through
a router or firewall.
If a computer from the local network offers server services,
for instance, the configuration of a router using NAT or IP
masquerading must forward the port used by the server
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