FRITZ!Box Fon WLAN 7113 112
Glossary
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
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 computer 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 computer 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 computer 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 computer via
remote management software like Symantec’s
