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Page 96 / 129 Scroll up to view Page 91 - 95
Advanced Settings
96
N600 Wireless Dual Band Gigabit Router Premium Edition WNDR3800
Port Forwarding to Permit External Host Communications
In both of the preceding examples, your computer initiates an application session with a
server computer on the Internet. However, you might need to allow a client computer on the
Internet to initiate a connection to a server computer on your network. Normally, your router
ignores any inbound traffic that is not a response to your own outbound traffic. You can
configure exceptions to this default rule by using the port forwarding feature.
A typical application of port forwarding can be shown by reversing the client-server
relationship from the previous Web server example. In this case, a remote computer’s
browser needs to access a Web server running on a computer in your local network. Using
port forwarding, you can tell the router, “When you receive incoming traffic on port 80 (the
standard port number for a Web server process), forward it to the local computer at
192.168.1.123.” The following sequence shows the effects of the port forwarding rule you
have defined:
1.
The user of a remote computer opens a browser and requests a Web page from
www.example.com, which resolves to the public IP address of your router. The remote
computer composes a Web page request message with the following destination
information:
Destination address
. The IP address of www.example.com, which is the address of your
router.
Destination port number
. 80, which is the standard port number for a Web server
process.
The remote computer then sends this request message through the Internet to your
router.
2.
Your router receives the request message and looks in its rules table for any rules covering
the disposition of incoming port 80 traffic. Your port forwarding rule specifies that incoming
port 80 traffic should be forwarded to local IP address 192.168.1.123. Therefore, your router
modifies the destination information in the request message:
The destination address is replaced with 192.168.1.123.
Your router then sends this request message to your local network.
3.
Your Web server at 192.168.1.123 receives the request and composes a return message
with the requested Web page data. Your Web server then sends this reply message to your
router.
4.
Your router performs Network Address Translation (NAT) on the source IP address, and
sends this request message through the Internet to the remote computer, which displays the
Web page from www.example.com.
To configure port forwarding, you need to know which inbound ports the application needs.
You usually can determine this information by contacting the publisher of the application or
the relevant user groups and newsgroups.
Page 97 / 129
Advanced Settings
97
N600 Wireless Dual Band Gigabit Router Premium Edition WNDR3800
How Port Forwarding Differs from Port Triggering
The following points summarize the differences between port forwarding and port triggering:
•
Port triggering can be used by any computer on your network, although only one
computer can use it at a time.
•
Port forwarding is configured for a single computer on your network.
•
Port triggering does require that you need to know the computer’s IP address in advance.
The IP address is captured automatically.
•
Port forwarding requires that you specify the computer’s IP address during configuration,
and the IP address can never change.
•
Port triggering requires specific outbound traffic to open the inbound ports, and the
triggered ports are closed after a period of no activity.
•
Port forwarding is always active and does not need to be triggered.
Set Up Port Forwarding to Local Servers
Using the port forwarding feature, you can allow certain types of incoming traffic to reach
servers on your local network. For example, you might want to make a local Web server, FTP
server, or game server visible and available to the Internet.
Use the Port Forwarding screen to configure the router to forward specific incoming protocols
to computers on your local network. In addition to servers for specific applications, you can
also specify a default DMZ server to which all other incoming protocols are forwarded.
Before starting, you need to determine which type of service, application, or game you want
to provide, and the local IP address of the computer that will provide the service. The server
computer has to always have the same IP address.
To set up port forwarding:
Tip:
To ensure that your server computer always has the same IP address,
use the reserved IP address feature of your WNDR3800 router.
Page 98 / 129
Advanced Settings
98
N600 Wireless Dual Band Gigabit Router Premium Edition WNDR3800
1.
Select
Advanced Setup > Port Forwarding/Port Triggering
to display the following
screen:
The Port Forwarding radio button is selected as the service type.
2.
From the Service Name list, select the service or game that you will host on your network. If
the service does not appear in the list, see
Add a Custom Service
on page 98.
3.
In the corresponding Server IP Address field, enter the last digit of the IP address of your
local computer that will provide this service.
4.
Click
Add
. The service appears in the list in the screen.
Add a Custom Service
To define a service, game, or application that does not appear in the Service Name list, you
have to first determine which port number or range of numbers is used by the application.
You can usually determine this information by contacting the publisher of the application or
user groups or newsgroups.
To add a custom service:
1.
Select
Advanced > Advanced Setup > Port Forwarding/Port Triggering
.
2.
Select the
Port Forwarding
radio button as the service type.
Page 99 / 129
Advanced Settings
99
N600 Wireless Dual Band Gigabit Router Premium Edition WNDR3800
3.
Click the
Add Custom Service
button to display the following screen:
4.
In the Service Name field, enter a descriptive name.
5.
In the Protoco
l
field, select the protocol. If you are unsure, select
TCP/UDP
.
6.
In the Starting Port field, enter the beginning port number.
•
If the application uses a single port, enter the same port number in the Ending Port
field.
•
If the application uses a range of ports, enter the ending port number of the range in
the Ending Port field.
7.
In the Server IP Address field, enter the IP address of your local computer that will provide
this service.
8.
Click
Apply
. The service appears in the list in the Port Forwarding/Port Triggering screen.
Editing or Deleting a Port Forwarding Entry
To edit or delete a port forwarding entry:
1.
In the table, select the radio button next to the service name.
2.
Click
Edit Service
or
Delete Service
.
Application Example: Making a Local Web Server Public
If you host a Web server on your local network, you can use port forwarding to allow Web
requests from anyone on the Internet to reach your Web server.
To make a local web server public:
1.
Assign your web server either a fixed IP address or a dynamic IP address using DHCP
address reservation. In this example, your router will always give your Web server an IP
address of 192.168.1.33.
Page 100 / 129
Advanced Settings
100
N600 Wireless Dual Band Gigabit Router Premium Edition WNDR3800
2.
In the Port Forwarding screen, configure the router to forward the HTTP service to the local
address of your Web server at
192.168.1.33
. HTTP (port 80) is the standard protocol for
Web servers.
3.
(Optional) Register a host name with a Dynamic DNS service, and configure your router to
use the name as described in
Dynamic DNS
on page 102. To access your Web server from
the Internet, a remote user has to know the IP address that has been assigned by your ISP.
However, if you use a Dynamic DNS service, the remote user can reach your server by a
user-friendly Internet name, such as mynetgear.dyndns.org.
Set Up Port Triggering
Port triggering is a dynamic extension of port forwarding that is useful in these cases:
•
More than one local computer needs port forwarding for the same application (but not
simultaneously).
•
An application needs to open incoming ports that are different from the outgoing port.
When port triggering is enabled, the router monitors outbound traffic looking for a specified
outbound “trigger” port. When the router detects outbound traffic on that port, it remembers
the IP address of the local computer that sent the data. The router then temporarily opens the
specified incoming port or ports, and forwards incoming traffic on the triggered ports to the
triggering computer.
While port forwarding creates a static mapping of a port number or range to a single local
computer, port triggering can dynamically open ports to any computer that needs them and
can close the ports when they are no longer needed.
Note:
If you use applications such as multiplayer gaming, peer-to-peer
connections, real-time communications such as instant messaging,
or remote assistance (a feature in Windows XP), you should also
enable Universal Plug and Play (UPnP) according to the instructions
in
Universal Plug and Play
on page 107.
To set up port triggering, you need to know which inbound ports the application needs. Also,
you need to know the number of the outbound port that will trigger the opening of the inbound
ports. You can usually determine this information by contacting the publisher of the
application or user groups or newsgroups.
To set up port triggering:
1.
Select
Advanced > Advanced Setup > Port Forwarding/Port Triggering
.

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