Fritz! Fon WLAN 7390 Installation, Configuration And Operation page 184

Glossary
Port forwarding
Private IP
address
FRITZ!Box Fon WLAN 7390
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 of
the atypical port numbers not required for normal opera-
tion of an application and offers specialized users the op-
portunity 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 settings of a router using NAT or IP mas-
querading 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 ad-
dress for all of the packets arriving at the port.
Typical server applications that require port forwarding
are FTP and Web servers. To allow access to a computer via
remote management software like Symantec pcAnywhere
or Microsoft's Remote Desktop, or even use of a file-shar-
ing program like eMule, the required ports must be re-
leased for port forwarding. Port forwarding settings for the
most important application cases are quite simple as long
as the settings of the router or the firewall already contain
rules with a corresponding preconfiguration.
Private IP addresses are used for computers and other
network devices within local IP networks.
Since many local IP networks are not connected to the In-
ternet except via single computers or routers (gateway),
certain address ranges are excluded from the publicly
available IP addresses so that they are available for as-
signment in local IP networks. An IP address may only be
assigned once within the local network. A private IP ad-
dress may exist in any number of other local networks.
184