Glossary
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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 (ma-
licious aplications 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
atypical port numbers not required for normal operation of
an application and offers specialized users the opportuni-
ty 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 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 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 computer via
remote management software like Symantec’s pcAny-
where or Microsoft’s Remote Desktop, or even use of a
file-sharing program like eDonkey, the required ports must
be released 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 Address
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.
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