Advanced Settings

56

WiFi Cable Modem Router C3700

The following screen displays:

Port Forwarding is selected as the service type.

2.

From the Service Name list, select the service or game that you host on your network. If the

service does not display in the list, see

Add a Custom Service

on page

56.

3.

In the corresponding Server IP Address field, enter the last digit of the IP address of your

local computer that provides this service.

4.

Click

Add

. The service displays in the list in the screen.

Add a Custom Service

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

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

newsgroups.



To add a custom service:

1.

From the Advanced tab, select

Advanced Setup > Port Forwarding/Port Triggering

.

2.

Select

Port Forwarding

as the service type.

3.

Click the

Add Custom Service

button.

Advanced Settings

57

WiFi Cable Modem Router C3700

The following screen displays:

4.

In the Service Name field, enter a descriptive name.

5.

In the Protoco

l

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

TCP/UDP

.

6.

In the Starting Port fields, 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 Internal IP Address field, enter the IP address of your local computer that provides this

service.

8.

Click the

Apply

button.

The service displays 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.

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 modem router always gives your web server

an IP address of 192.168.0.33.

Advanced Settings

58

WiFi Cable Modem Router C3700

2.

In the Port Forwarding/Port Triggering screen, configure the modem router to forward the

HTTP service to the local address of your web server at

192.168.0.33

. HTTP (port 80) is the

standard protocol for web servers.

3.

(Optional) Register a host name with a Dynamic DNS service, and configure your modem

router to use the name as described in

Dynamic DNS

on page

60. To access your web

server from the Internet, a remote user must know the IP address that your ISP assigns.

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 opens incoming ports that are different from the outgoing port.

When port triggering is enabled, the modem router monitors outbound traffic looking for a

specified outbound “trigger” port. When the modem router detects outbound traffic on that

port, it remembers the IP address of the local computer that sent the data. The modem 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), enable Universal

Plug and Play (UPnP) according to the instructions in

Remote

Management

on page

61.

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 triggers 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.

From the Advanced tab, select

Advanced Setup > Port Forwarding/Port Triggering

.

Advanced Settings

59

WiFi Cable Modem Router C3700

2.

Select the

Port Triggering

radio button.

3.

Clear the

Disable Port Triggering

check box if it is selected.

Note:

If the Disable Port Triggering check box is selected after you configure

port triggering, port triggering is disabled. However, any port triggering

configuration information you added to the modem router is retained even

though it is not used.

4.

In the Port Triggering Time-out field, enter a value up to 9999 minutes.

5.

This value controls the inactivity timer for the designated inbound ports. The inbound ports

close when the inactivity time expires. This step is required because the modem router

cannot be sure when the application has terminated.

6.

Click the

Add Service

button.

The following screen displays:

Advanced Settings

60

WiFi Cable Modem Router C3700

7.

In the Service Name field, type a descriptive service name. No spaces are allowed for the

service name field.

8.

In the Service User list, select

Any

(the default) to allow any computer on the Internet to use

this service. Otherwise, select

Single address

, and enter the IP address of one computer to

restrict the service to a particular computer.

9.

Select the service type, either

TCP

or

UDP

or both (

TCP/UDP

). If you are not sure, select

TCP/UDP.

10.

In the Triggering Port field, enter the number of the outbound traffic port that causes the

inbound ports open.

11.

Enter the inbound connection port information in the Connection Type, Starting Port, and

Ending Port fields.

12.

Click the

Apply

button.

The service displays in the Port Triggering Portmap table.

Dynamic DNS

If your Internet service provider (ISP) gave you a permanently assigned IP address, you can

register a domain name and have that name linked with your IP address by public Domain

Name Servers (DNS). However, if your Internet account uses a dynamically assigned IP

address, you do not know in advance what your IP address is, and the address can change

frequently. In this case, you can use a commercial Dynamic DNS service. This type of service

lets you register your domain to their IP address and forwards traffic directed at your domain

to your frequently changing IP address.

If your ISP assigns a private WAN IP address (such as 192.168.x.x or 10.x.x.x), the Dynamic

DNS service does not work because private addresses are not routed on the Internet.

Your modem router contains a client that can connect to the Dynamic DNS service that

DynDNS.org provided. First visit their website at

and obtain an

account and host name that you configure in the modem router. Then, whenever your

ISP-assigned IP address changes, your modem router automatically contacts the Dynamic

DNS service provider, logs in to your account, and registers your new IP address. If your host

name is hostname, for example, you can reach your modem router at

.



To set up Dynamic DNS:

1.

From the Advanced tab, select

Advanced Setup > Dynamic DNS

.