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61
Configuring the Advanced Settings
Setting up the NAT function
Your Gigaset SE551 WLAN dsl/cable comes provided with the NAT (Network Address
Translation) function. With Address Mapping, several users on your local network can
access the Internet via one or more public IP addresses. In the default setting, all the
local IP address are mapped to your router's public IP address.
One feature of NAT is that data from the Internet is not allowed into your local network
unless it has been explicitly requested by one of the PCs on that network. Most Internet
applications run behind the NAT firewall without any problems. If you request Internet
pages, for example, or send and receive e-mails, the request for data from the Internet
comes from a PC on the local network and so the router allows the data through. The
router opens exactly
one
port for the application. A port is an internal PC address
through which the data is exchanged between a server on the Internet and a client on
a PC in the local network. Communicating via a port follows the rules of a particular pro-
tocol (TCP or UDP).
If an external application tries to send a call to a PC within 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 the user on
the local network. These applications cannot work if Network Address Translation (NAT)
has been activated.
Using port forwarding (the forwarding of requests to particular ports) you make the
router forward requests from the Internet for a certain service, e.g a game, to the appro-
priate port or ports on the PC on which the game is running.
Port triggering is a specific variant of port forwarding. Unlike port forwarding, in this
case the Gigaset SE551 WLAN dsl/cable forwards data from the set port block to the PC
which has previously sent data to the Internet via a certain port (trigger port). This
means that approval for the data transfer is not tied to one specific PC in your network,
but only to the port numbers of the required Internet service.
Where configuration is concerned, this means:
u
You have to define a so-called trigger port for the application and also the protocol
(TCP or UDP) that this port uses. Then you assign to this trigger port the public ports
that have to be opened for the application.
u
The router checks all outgoing data for the port number and protocol. If it recognises
a match of port and protocol to a defined trigger port, then it will open the assigned
public ports and notes the IP address of the PC that sent the data. If data comes back
from the Internet via one of these public ports, it allows the data through and directs
it to the right PC. A trigger event always comes from a PC within the local network.
If a trigger port is addressed from outside, it is simply ignored by the router.
Page 62 / 148
62
Configuring the Advanced Settings
When the Gigaset SE551 WLAN dsl/cable is supplied, the
NAT
function (Network Address
Translation) is activated, i.e. all IP addresses of PCs in the local network are converted to
the router's public IP address when accessing the Internet.
You can use the NAT settings for the Gigaset SE551 WLAN dsl/cable to
u
set up port triggering for special applications (see page 63),
u
set up the Gigaset SE551 WLAN dsl/cable as a virtual server by configuring Port For-
warding (see page 64),
u
open the firewall for selected PCs (see page 65).
You can activate or deactivate the NAT function (default setting: NAT function is acti-
vated).
ì
In the
Advanced Settings
Internet
menu, select
Address Translation (NAT)
and
select the required option.
Please remember:
u
An application that is configured for port triggering can only be run by one user in
the local network at a time.
u
As long as the public ports are open, they can be used by unauthorised persons to
gain access to a PC in the local network.
Please remember:
For the functions described below you must make sure that the IP addresses of the
PCs do not change. If the IP addresses of the PCs are assigned via the DHCP server
of the Gigaset SE551 WLAN dsl/cable, you must select the option
Never expires
(see page 70) for the settings on the
Local Network
screen for
Lease time
or assign
static IP addresses for the PCs.
Page 63 / 148
63
Configuring the Advanced Settings
Port Triggering
If you configure Port Triggering for a certain application, determine a so-called trigger
port and the protocol (TCP or UDP) this port uses. Then you assign to this trigger port
the public ports that have to be opened for the application.
You can select known Internet services for this or assign ports or blocks of ports manu-
ally.
ì
To set up port triggering for a service, in the
Address Translation (NAT)
menu,
select
Port Triggering
.
ì
Select the required application from the
Predefined applications
list.
ì
Click the
Add
button. The data for the required service is entered on the screen.
ì
Select the option in the
Enabled
column.
If the application you require is not in the list, then you must enter the relevant data on
the screen manually:
ì
Local protocol
: Select the protocol that is to be monitored for outgoing traffic.
ì
Local port
: Enter the port that is to be monitored for outgoing traffic.
ì
Public protocol
: Select the protocol that is to be allowed for incoming data traffic.
ì
Public port
: Enter the port that is to be opened for incoming traffic.
ì
Comment
: Enter a description to help you identify different entries.
Note:
You can enter a single port number, several individual port numbers separated by
commas, port blocks consisting of two port numbers separated by a dash, or any
combination of these, e.g.
80,90-140,180
).
Page 64 / 148
64
Configuring the Advanced Settings
ì
Select the option in the
Enabled
column.
ì
Click on the
Delete
button to delete an entry. Click on the
Add
button to add a new
entry.
ì
Apply the settings by clicking
OK
.
Port Forwarding
If you configure Port Forwarding, the Gigaset SE551 WLAN dsl/cable outwardly assumes
the role of the servers. It receives requests from remote users under its public IP address
and automatically redirects them to local PCs. The private IP addresses of the servers on
the local network remain protected.
Internet services are addressed via defined port numbers. The Gigaset SE551 WLAN dsl/
cable needs a mapping table of the port numbers to redirect the service requests to the
server that actually provides the service. For this, Port Forwarding has to be configured.
ì
To set up port forwarding for a service, select
Port Forwarding
in the
Address Translation (NAT)
menu.
ì
Select the required application from the
Predefined applications
list.
ì
Click the
Add
button. The data for the required service is entered on the screen.
ì
Select the option in the
Enabled
column.
If the application you require is not in the list, then you must enter the relevant data on
the screen manually:
ì
Select the protocol of the service you are providing from the
Protocol
list.
ì
Under
Public port,
enter the port number of the service you are providing.
ì
In the
Local port
field, enter the internal port number to which service requests are
to be forwarded.
Page 65 / 148
65
Configuring the Advanced Settings
ì
In the
Local IP address
field, enter the IP address of the PC which provides the serv-
ice.
Example: the Web server has been configured to react to requests on port 8080.
However, the requests from websites enter by port 80 (standard value). If you add
the PC to the forwarding table and define port 80 as the public port and Port 8080
as an internal port, all requests from the Internet are diverted to the service with the
port number 80 on the Web server of the PC you have defined with port 8080.
ì
Click on
Add
.
ì
Click on
Delete
if you wish to delete the data in the relevant line again.
ì
Select the option in the
Enabled
column.
ì
Click
OK
to apply the settings.
Opening the firewall for selected PCs (Exposed Host)
You can set up a client in your local network to be an exposed host. Your device will
them forward all incoming data traffic from the Internet to this client. You can then, for
example, operate your own Web server on one of the clients in your local network and
make it accessible to Internet users.
As the exposed host your local client is directly visible to the Internet and therefore par-
ticularly exposed to risk (e.g. from hacker attacks). You should only activate this func-
tion if it is absolutely necessary (e.g. to operate a Web server) and other functions
(e.g. port forwarding) are not adequate. In this case you should take appropriate meas-
ures on the clients concerned.
ì
To set up a PC as Exposed Host, select
Exposed Host
in the
Address Translation
(NAT)
menu.
Note:
You can enter a single port number, several individual port numbers separated by
commas, port blocks consisting of two port numbers separated by a dash, or any
combination of these, e.g.
80,90-140,180
).
Please remember:
Only one PC per public IP address can be set up as Exposed Host (see also the section
"Port Forwarding" on page 64.

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