Netgear Dgnd4000 N750 Wireless Dual Band Gigabit Adsl2 Plus Modem Router User Manual

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111  N750 Wireless Dual Band Gigabit ADSL Modem Router DGND4000
the wireless modem router to open additional incoming ports when a particular outgoing port 
originates a session.
An example is Internet Relay Chat (IRC). Your computer connects to an IRC server at 
destination port 6667. The IRC server not only responds to your originating source port, but 
also sends an “identify” message to your computer on port 113. Using port triggering, you can 
tell the wireless modem router, “When you initiate a session with destination port 6667, you 
have to also allow incoming traffic on port 113 to reach the originating computer.” Using steps 
similar to the preceding example, the following sequence shows the effects of the port 
triggering rule you have defined:
1. You open an IRC client program to start a chat session on your computer. 
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 wireless modem router.
3. Your wireless modem router creates an entry in its internal session table describing this 
communication session between your computer and the IRC server. Your wireless modem 
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 wireless modem 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 wireless modem router using the 
NAT-assigned source port (as in the previous example, say port 33333) as the destination 
port. The IRC server also sends an identify message to your wireless modem router with 
destination port 113.
6. Upon receiving the incoming message to destination port 33333, your wireless modem 
router checks its session table to determine whether there is an active session for port 
number 33333. Finding an active session, the wireless modem 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 wireless modem router 
checks its session table and learns that there is an active session for port 113 associated 
with your computer. The wireless modem 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 wireless modem router eventually senses a period 
of inactivity in the communications. The wireless modem 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 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.
Note:Only one computer at a time can use the triggered application. 
						

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112 N750 Wireless Dual Band Gigabit ADSL Modem Router DGND4000 
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 wireless 
modem 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 wireless modem 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 wireless modem 
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 
wireless modem 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 
wireless modem router.
2. Your wireless modem 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 wireless modem router modifies the destination information in the request 
message:
The destination address is replaced with 192.168.1.123.
Your wireless modem 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 
wireless modem router.
4. Your wireless modem 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. 
Usually you can determine this information by contacting the publisher of the application or 
the relevant user groups and 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 requires that you 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/Port Triggering screen to configure the wireless modem 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 provides 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 N750 Modem 
Router.  
						

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1. 
Select  ADVANCED > Advanced Setup > Port Forwarding/Port Triggering.
Port Forwarding is selected as the service type.
2.  Click  Add.
3. From the Service list, select the service or game that you host on your \
network. If the service 
does not appear in the list, see  Add a Custom Service on page 11 5.
4.  From the 
 Action list, select the action that you want.
5.  In the Send to LAN Server field, enter the last digit of the IP address \
of your local computer 
that provides this service. 
6.  Click  Apply . 
 The service appears in the list in the screen. 
						

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Add a Custom Service
To define a service, game, or application that does not appear in the Ser\
vice 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  ADV
 ANCED > Advanced Setup > Port Forwarding/Port Triggering .
2.  Select  Port Forwarding  as the service type.
3.  Click the  Add Custom Service button.
4. In the Name field, enter a descriptive name. 
5.  In the 
Type list, select the protocol. If you are unsure, select  TCP/UDP.
6.  In the Start Port field, enter the beginning port number
 . 
• If the application uses a single port, enter the same port number in the\
 End Port field.
• If the application uses a range of ports, enter the ending port number o\
f the range in 
the End Port field.
7.  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  ADV
 ANCED > Advanced Setup > Port Forwarding/Port Triggering .
2.  In the table, select the radio button next to the service name.
3.  Click  Edit Service or  Delete Service. 
						

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116 N750 Wireless Dual Band Gigabit ADSL Modem Router DGND4000 
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 wireless modem router always gives your 
web server an IP address of 192.168.1.33. 
2. In the Port Forwarding/Port Triggering screen, configure the wireless modem 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 wireless 
modem router to use the name as described in 
Dynamic DNS on page 11 8. To access your 
web server from the Internet, a remote user has to know the IP address 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 wireless modem router monitors outbound traffic looking 
for a specified outbound “trigger” port. When the wireless modem router detects outbound 
traffic on that port, it remembers the IP address of the local computer that sent the data. The 
wireless modem 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 dynamically opens 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 123.
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. 
						

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To set up port triggering: 
1. 
Select  ADV
 ANCED > Advanced Setup > Port Forwarding/Port Triggering .
2.  Select the Port T
 riggering radio button to display the port triggering information.
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 triggeri\
ng 
configuration information you added to the wireless modem router is 
retained even though it is not used.
4.  In the Port 
 Triggering Timeout field, enter a value up to 9999 minutes. 
This value controls the inactivity timer for the designated inbound port\
s. The inbound  ports close when the inactivity time expires. 
 This closure is required because the wireless 
modem router cannot be sure when the application has terminated. 
						

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5. 
Click  Add Service.
6. In the Service Name field, type a descriptive service name. 
7.  In the Service User list, select  Any (the default) to allow this service to be used by any 
computer on the Internet. Otherwise, select  Single address, and enter the IP address of 
one computer to restrict the service to a particular computer

. 
8.  Select the service type, either  TCP or UDP or both ( TCP/UDP). If you are not sure, select 
TCP/UDP
 .
9.  In the 
Triggering Port field, enter the number of the outbound traffic port that causes the 
inbound ports to be opened. 
10.  Enter the inbound connection port information in the Service 
 Type, Starting Port, and Ending 
Port fields.
11.  Click  Apply . 
 The service appears in the Port Triggering Portmap table. 
Dynamic DNS
If your Internet service provider (ISP) gave you a permanently assigne\
d 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 add\
ress 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 works because private addresses are not routed on t\
he Internet.
Your wireless modem router contains a client that can connect to the Dyna\
mic DNS service  provided by DynDNS.org. First visit their website at http://www
 .dyndns.org and obtain an  
						

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 N750 Wireless Dual Band Gigabit ADSL Modem Router DGND4000
account and host name that you configure in the wireless modem router. Then, whenever 
your ISP-assigned IP address changes, your wireless modem router automat\
ically 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 \
wireless modem 
router at http://hostname.dyndns.org.
On the Advanced tab, select 
Advanced Setup > Dynamic DNS.
To set up Dynamic DNS:
1. Register for an account with one of the Dynamic DNS service providers wh\
ose 
addresses appear in the Service Provider list.
2.  Select the Use a Dynamic DNS Service  check box. 
3.  Select the address of your Dynamic DNS service provider
 . For example, for DynDNS.org, 
select  www.dyndns.org .
4.  T
ype the host name (or domain name) that your Dynamic DNS service provi\
der gave you.
5. T
ype the user name for your Dynamic DNS account. This is the name that you use to log in 
to your account, not your host name.
6.  T
ype the password (or key) for your Dynamic DNS account. 
7.  Click  Apply to save your configuration.
Static Routes
Static routes provide additional routing information to your wireless mo\
dem router. Under 
usual circumstances, the wireless modem router has adequate routing info\
rmation after it 
has been configured for Internet access, and you do not need to configur\
e additional static 
routes. You have to configure static routes only for unusual cases such as multip\
le wireless 
modem routers or multiple IP subnets on your network. 
						

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As an example of when a static route is needed, consider the following c\
ase:
• Y
our primary Internet access is through a cable modem to an ISP.
•Y
ou have an ISDN wireless modem router on your home network for connectin\
g to the 
company where you are employed. This wireless modem router’s address on your LAN is 
192.168.1.100.
• Y
our company’s network address is 134.177.0.0.
When you first configured your wireless modem router, two implicit stati\
c routes were 
created. 

A default route was created with your ISP as the gateway, and a second static route 
was created to your local network for all 192.168.1.x addresses. With th\
is configuration, if you 
attempt to access a device on the 134.177.0.0 network, your wireless mod\
em router forwards 
your request to the ISP. The ISP forwards your request to the company where you are 
employed, and the request is likely to be denied by the company’s firewall.
In this case you have to define a static route, telling your wireless mo\
dem router that 
134.177.0.0 should be accessed through the ISDN wireless modem router at\
 192.168.1.100. 
In this example:
• The Destination IP 
 Address and IP Subnet Mask fields specify that this static route 
applies to all 134.177.x.x addresses. 
• The Gateway IP 
 Address field specifies that all traffic for these addresses should be 
forwarded to the ISDN wireless modem router at 192.168.1.100. 
• A metric value of 1 works since the ISDN wireless modem router is on the\
 LAN. 
• Private is selected only as a precautionary security measure in case RIP\
 is activated.
To set up a static route:
1. Select  ADV
 ANCED > Advanced Setup > Static Routes .
2.  Click  Add.