Setting up the nat function – Siemens SX763 User Manual

Page 65

Configuring Advanced Settings

Gigaset SX763 WLAN dsl / en / A31008-M707-R131-2-7619 / configure_router.fm / 08.12.2006

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– Specify IP address or Specify MAC address: The rule applies to a PC you have

selected via the IP address or MAC address.

Enter a name for the Comment for the access rule.

Define the Access level.
You can choose Deny access to the Internet or Allow web browsing. If you select
Custom, you can make the following settings:

If you wish to create a Service filter, choose one of the following options.
– In Filtering mode, specify whether the selected services are to be allowed or

blocked.

– Select the Services that are to be allowed or blocked.

Select the Protocol and enter the appropriate Port (a single port number,

several port numbers separated by commas, port blocks consisting of two port

numbers separated by a dash, or any combination of these, for example 80,90-
140,180

). The Description that is displayed helps you to identify different serv-

ices.

– You can also select services from the Predefined applications list.
– Click Add to create a new entry with the entered data or for the selected, prede-

fined application.

– Click Delete to delete an entry.

Click OK to apply the settings.

Setting up the NAT function

The Gigaset SX763 WLAN dsl comes equipped with the NAT (Network Address Transla-
tion) function. With address mapping, several users in the local network can access the
Internet via one or more public IP addresses. All the local IP addresses are assigned to
the router's public IP address by default.
One of the characteristics of NAT is that data from the Internet is not allowed into the
local network unless it has been explicitly requested by one of the PCs in the network.
Most Internet applications can run behind the NAT firewall without any problems. For
example, if you request Internet pages or send and receive e-mails, the request for data
from the Internet comes from a PC in the local network, and so the router allows the
data through. The router opens precisely one port for the application. A port in this con-
text is an internal PC address, via which the data is exchanged between the Internet and
a client on a PC in the local network. Communicating via a port is subject to the rules of
a particular protocol (TCP or UDP).
If an external application tries to send a call to a PC in the local network, the router will
block it. There is no open port via which the data could enter the local network.
Some applications, such as games on the Internet, require several links, i.e. several ports
so that the players can communicate with each other. In addition, these applications
must also be permitted to send requests from other users on the Internet to users in the
local network. These applications cannot be run if Network Address Translation (NAT)
has been activated.