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2.

Your IRC client composes a request message to an IRC server using a destination port

number of 6667, the standard port number for an IRC server process. Your computer then

sends this request message to your router.

3.

Your router creates an entry in its internal session table describing this communication

session between your computer and the IRC server. Your router stores the original

information, performs Network Address Translation (NAT) on the source address and port,

and sends this request message through the Internet to the IRC server.

4.

Noting your port triggering rule and having observed the destination port number of 6667,

your router creates an additional session entry to send any incoming port 113 traffic to your

computer.

5.

The IRC server sends a return message to your router using the NAT-assigned source port

(for example, port 33333) as the destination port. The IRC server also sends an “identify”

message to your router with destination port 113.

6.

Upon receiving the incoming message to destination port 33333, your router checks its

session table to determine whether there is an active session for port number 33333.

Finding an active session, the router restores the original address information replaced by

NAT and sends this reply message to your computer.

7.

Upon receiving the incoming message to destination port 113, your router checks its session

table and learns that there is an active session for port 113 associated with your computer.

The router replaces the message’s destination IP address with your computer’s IP address

and forwards the message to your computer.

8.

When you finish your chat session, your router eventually senses a period of inactivity in the

communications. The router then removes the session information from its session table,

and incoming traffic is no longer accepted on port numbers 33333 or 113.

To configure 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 the relevant user groups or news groups.

Only one computer at a time can use the triggered application.

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

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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 or news groups.

How Port Forwarding Differs from Port Triggering

The following points summarize the differences between port forwarding and port triggering:

•

Any computer on your network can use port triggering, although only one computer can

use it at a time.

•

Port forwarding is configured for a single computer on your network.

•

With port triggering, the router 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 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.

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Set Up Port Forwarding to Local Servers

The port forwarding feature lets you 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/Port Triggering 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 you start, 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 ensure that your server computer always has the same IP address, use the reserved IP

address feature of your product. See

Set up Address Reservation

on page

38.



To forward specific incoming protocols:

1.

Select

Advanced > Advanced Setup > Port Forwarding/Port Triggering

.

2.

Leave the

Port Forwarding

radio button selected as the service type.

3.

Click the

Add

button.

4.

In the Service Name list, select the service name.

If the service does not appear in the list, see

Add a Custom Service

on page

68

5.

Fill in the Server IP Address field.

6.

Click

Add

.

The service appears in the list on the Port Forwarding screen.

Add a Custom Service

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

determine which port number or range of numbers the application uses. You can usually

determine this information by contacting the publisher of the application or user groups or

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

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AC1450 Smart WiFi Router



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.

3.

Click the

Add Custom Service

button.

4.

In the Service Name field, enter a descriptive name.

5.

In the Service Type field, select the protocol. If you are unsure, select

TCP/UDP

.

6.

In the External 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 External Ending Port field.

7.

Specify the internal ports by one of these methods:

•

Leave the

Use the same port range for Internal port

check box selected.

•

Fill in the Internal Starting Port and Internal Ending Port fields.

8.

Fill in the Internal IP address field, or select the radio button for an attached device listed in

the table.

9.

Click

Apply

.

The service appears in the list in the Port Forwarding/Port Triggering screen.

Edit or Delete a Port Forwarding Entry



To edit or delete a port forwarding entry:

1.

Select

Advanced > Advanced Setup > Port Forwarding/Port Triggering

.

2.

Select the

Port Forwarding

radio button as the service type

3.

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

4.

Click

Edit Service

or

Delete Service

.

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Application Example: Make 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 always gives your web server an IP address of 192.168.1.33.

2.

In the Port Forwarding/Port Triggering 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.

To access your web server from the Internet, a remote user has to know the IP address

that your ISP assigned. 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.

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).

Universal Plug and Play

on

page

100.