FRITZ!Box Fon WLAN 7113
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Glossary
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
numbers can be specified. Ports up to port number 1,024
are reserved 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
protecting 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 services. This is also a way of
preventing any Trojans that may have infected your
computer from receiving data on ports it created as means
of accessing your PC for potentially damaging activities. A
firewall blocks most atypical port numbers not required
for normal operation of an application and offers
specialized users the opportunity to forward specified
ports.
port forwarding
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 PC from the local network offers server services, for
instance, the settings of a router using NAT or IP
masquerading must enable or forward the port used by
the server service for access to incoming data packets and
thus keep it open permanently. The private IP address of
the given PC must be saved as the destination address for
all of the packets arriving at the port.
Typical server applications which require port forwarding
are FTP and Web servers. To allow access to a PC via
remote management software like Symantec pcAnywhere
or Microsoft's Remote Desktop, or even use of a file-
