NETGEAR Wireless-N Router WNR2000 User Manual

Fine-Tuning Your Network

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How Port Forwarding Changes the Communication Process

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 our 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 Internet Explorer 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:

•

The destination address is the IP address of www.example.com, which is the address of

your router.

•

The destination port number is 80, 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 user

groups or newsgroups.

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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 not 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 must 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.

Configuring 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 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. The DMZ

server is configured in the WAN Setup screen, as discussed in

“Setting Up a Default DMZ Server”

on page 4-8

.

Before starting, you need to determine which type of service, application, or game you will

provide, and the local IP address of the computer that will provide the service. Be sure the

computer’s IP address never changes.

Tip:

To ensure that your server computer always has the same IP address, use the

reserved IP address feature of your WNR2000 router. See

“Using Address

Reservation” on page 4-5

for instructions on how to use reserved IP addresses.

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To configure port forwarding to a local server:

1.

Select

Port Forwarding/Port Triggering

under Advanced in the main menu. The Port

Forwarding/Port Triggering screen displays.

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 the following section,

“Adding a Custom

Service

.”

3.

In the corresponding

Server IP Address

fields, enter the last digit of the IP address of your

local computer that will provide this service.

4.

To the right of Server IP Address, click

Add

. The service appears in the list in the screen.

Adding a Custom Service

To define a service, game, or application that does not appear in the Service Name list, you must

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. When you have the port number information, follow these steps:

1.

Select

Port Forwarding/Port Triggering

under Advanced in the main menu.

Figure 5-1

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2.

Click

Add Service

(see

Figure 5-1 on page 5-7

).The Ports–Custom Services screen displays.

3.

In the

Service Name

field, enter a descriptive name.

4.

In the

Service Type

field, select the protocol. If you are unsure, select

TCP/UDP

.

5.

In the

Starting Port

field, enter the beginning port number.

•

If the application uses only 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.

6.

In the

Server IP Address

field, enter the IP address of your local computer that will provide

this service.

7.

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:

Figure 5-2

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1.

In the table, select the button next to the service name.

2.

Click

Edit Service

or

Delete Service

to make changes.

3.

Click

Apply

.

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, as explained in

“Using Address Reservation” on page 4-5

. In this example, your

router will always give your Web server an IP address of 192.168.1.33.

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

“Using a Dynamic DNS Service” on page 4-6

.

To access your Web server from the Internet, a remote user must 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.

Configuring 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.

Figure 5-3