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The following table describes the labels in this screen.
14.3
Port Forwarding Screen
Use this
screen to forward incoming service requests to the server(s) on your local network and set
a default server. You may enter a single port number or a range of port numbers to be forwarded,
and the local IP address of the desired server. The port number identifies a service; for example,
web service is on port 80 and FTP on port 21. In some cases, such as for unknown services or
where one server can support more than one service (for example both FTP and web service), it
might be better to specify a range of port numbers.
In addition to the servers for specified services, NAT supports a default server. A service request
that does not have a server explicitly designated for it is forwarded to the default server. If the
default is not defined, the service request is simply discarded.
Note: Many residential broadband ISP accounts do not allow you to run any server
processes (such as a Web or FTP server) from your location. Your ISP may
periodically check for servers and may suspend your account if it discovers any
active services at your location. If you are unsure, refer to your ISP.
Port forwarding allows you to define the local servers to which the incoming services will be
forwarded. To change your NBG6716’s port forwarding settings, click
Network > NAT
>
Port
Forwarding
. The screen appears as shown.
Note: If you do not assign a
Default Server
, the NBG6716 discards all packets received
for ports that are not specified in this screen or remote management.
Refer to
Appendix C on page 218
for port numbers commonly used for particular services.
Table 50
Network > NAT > General
LABEL
DESCRIPTION
Network Address
Translation (NAT)
Network Address Translation (NAT) allows the translation of an Internet protocol
address used within one network (for example a private IP address used in a local
network) to a different IP address known within another network (for example a public
IP address used on the Internet).
Select
Enable
to activate NAT. Select
Disable
to turn it off.
Apply
Click
Apply
to save your changes back to the NBG6716.
Cancel
Click
Cancel
to begin configuring this screen afresh.
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Chapter 14 NAT
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Figure 80
Network > NAT > Port Forwarding
The following table describes the labels in this screen.
Table 51
Network > NAT > Port Forwarding
LABEL
DESCRIPTION
Default Server Setup
Default Server
In addition to the servers for specified services, NAT supports a default server. A default
server receives packets from ports that are not specified in the
Port Forwarding
screen. You can decide whether you want to use the default server or specify a server
manually.
Select this to use the default server.
Change to Server
Select this and manually enter the server’s IP address.
Service Name
Select a pre-defined service from the drop-down list box. The pre-defined service port
number(s) and protocol will be displayed in the port forwarding summary table.
Otherwise, select
User define
to manually enter the port number(s) and select the IP
protocol.
Service Protocol
Select the transport layer protocol supported by this virtual server. Choices are
TCP
,
UDP
, or
TCP_UDP
.
If you have chosen a pre-defined service in the
Service Name
field, the protocol will be
configured automatically.
Server IP Address
Enter the inside IP address of the virtual server here and click
Add
to add it in the port
forwarding summary table.
#
This is the number of an individual port forwarding server entry.
Status
This icon is turned on when the rule is enabled.
Name
This field displays a name to identify this rule.
Protocol
This is the transport layer protocol used for the service.
Port
This field displays the port number(s).
Server IP Address
This field displays the inside IP address of the server.
Modify
Click the
Edit
icon to open the edit screen where you can modify an existing rule.
Click the
Delete
icon to remove a rule.
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14.3.1
Port Forwarding Edit Screen
This screen lets you edit a port forwarding rule. Click a rule’s
Edit
icon in the
Port Forwarding
screen to open the following screen.
Figure 81
Network > NAT > Port Forwarding Edit
The following table describes the labels in this screen.
Apply
Click
Apply
to save your changes back to the NBG6716.
Cancel
Click
Cancel
to begin configuring this screen afresh.
Table 51
Network > NAT > Port Forwarding (continued)
LABEL
DESCRIPTION
Table 52
Network > NAT > Port Forwarding Edit
LABEL
DESCRIPTION
Port Forwarding
Select
Enable
to turn on this rule and the requested service can be forwarded to the host
with a specified internal IP address.
Select
Disable
to disallow forwarding of these ports to an inside server without having to
delete the entry.
Service Name
Type a name (of up to 31 printable characters) to identify this rule in the first field next to
Service Name
. Otherwise, select a predefined service in the second field next to
Service
Name
. The predefined service name and port number(s) will display in the
Service Name
and
Port
fields.
Protocol
Select the transport layer protocol supported by this virtual server. Choices are
TCP
,
UDP
,
or
TCP_UDP
.
If you have chosen a pre-defined service in the
Service Name
field, the protocol will be
configured automatically.
Port
Type a port number(s) to define the service to be forwarded to the specified server.
To specify a range of ports, enter a hyphen (-) between the first port and the last port,
such as 10-.
Server IP
Address
Type the IP address of the server on your LAN that receives packets from the port(s)
specified in the
Port
field.
Back
Click
Back
to return to the previous screen.
Apply
Click
Apply
to save your changes back to the NBG6716.
Cancel
Click
Cancel
to begin configuring this screen afresh.
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14.4
Port Trigger Screen
To change your NBG6716’s trigger port settings, click
Network > NAT > Port Trigger
. The screen
appears as shown.
Note: Only one LAN computer can use a trigger port (range) at a time.
Figure 82
Network > NAT > Port Trigger
The following table describes the labels in this screen.
Table 53
Network > NAT > Port Trigger
LABEL
DESCRIPTION
#
This is the rule index number (read-only).
Name
Type a unique name (up to 15 characters) for identification purposes. All characters are
permitted - including spaces.
Incoming
Incoming is a port (or a range of ports) that a server on the WAN uses when it sends out
a particular service. The NBG6716 forwards the traffic with this port (or range of ports) to
the client computer on the LAN that requested the service.
Port
Type a port number or the starting port number in a range of port numbers.
End Port
Type a port number or the ending port number in a range of port numbers.
Trigger
The trigger port is a port (or a range of ports) that causes (or triggers) the NBG6716 to
record the IP address of the LAN computer that sent the traffic to a server on the WAN.
Port
Type a port number or the starting port number in a range of port numbers.
End Port
Type a port number or the ending port number in a range of port numbers.
Apply
Click
Apply
to save your changes back to the NBG6716.
Cancel
Click
Cancel
to begin configuring this screen afresh.
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14.5
Technical Reference
The following section contains additional technical information about the NBG6716 features
described in this chapter.
14.5.1
NATPort Forwarding: Services and Port Numbers
A port forwarding set is a list of inside (behind NAT on the LAN) servers, for example, web or FTP,
that you can make accessible to the outside world even though NAT makes your whole inside
network appear as a single machine to the outside world.
Use the
Port Forwarding
screen to forward incoming service requests to the server(s) on your
local network. You may enter a single port number or a range of port numbers to be forwarded, and
the local IP address of the desired server. The port number identifies a service; for example, web
service is on port 80 and FTP on port 21. In some cases, such as for unknown services or where one
server can support more than one service (for example both FTP and web service), it might be
better to specify a range of port numbers.
In addition to the servers for specified services, NAT supports a default server. A service request
that does not have a server explicitly designated for it is forwarded to the default server. If the
default is not defined, the service request is simply discarded.
Note: Many residential broadband ISP accounts do not allow you to run any server
processes (such as a Web or FTP server) from your location. Your ISP may
periodically check for servers and may suspend your account if it discovers any
active services at your location. If you are unsure, refer to your ISP.
14.5.2
NAT Port Forwarding Example
Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (
A
in the example),
port 80 to another (
B
in the example) and assign a default server IP address of 192.168.1.35 to a
third (
C
in the example). You assign the LAN IP addresses and the ISP assigns the WAN IP address.
The NAT network appears as a single host on the Internet.
Figure 83
Multiple Servers Behind NAT Example

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