Netgear D6200 Wifi Dsl Modem Router User Manual

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111  D6200 WiFi DSL Modem Router
Remote Computer Access Basics
When a computer on your network needs to access a computer on the Internet, your 
computer sends your WiFi DSL modem router a message containing the source and 
destination address and process information. Before forwarding your message to the remote 
computer, your WiFi DSL modem router has to modify the source information and create and 
track the communication session so that replies can be routed back to your computer. 
Here is an example of normal outbound traffic and the resulting inbound responses:
1. You open a browser, and your operating system assigns port number 5678 to this 
browser session. 
2. You type http://www.example.com into the URL field, and your computer creates a web 
page request message with the following address and port information. The request 
message is sent to your WiFi DSL modem router.
•Source address. Your computer’s IP address.
•Source port number. 5678, which is the browser session. 
•Destination address. The IP address of www.example.com, which your computer 
finds by asking a DNS server.
•Destination port number. 80, which is the standard port number for a web server 
process.
3. Your WiFi DSL modem router creates an entry in its internal session table describing this 
communication session between your computer and the web server at www.example.com. 
Before sending the web page request message to www.example.com, your WiFi DSL 
modem router stores the original information and then modifies the source information in the 
request message, performing Network Address Translation (NAT):
•The source address is replaced with your WiFi DSL modem router’s public IP 
address. This requirement is necessary because your computer uses a private IP 
address that is not globally unique and cannot be used on the Internet.
•The source port number is changed to a number chosen by the WiFi DSL modem 
router, such as 33333. This requirement is necessary because two computers could 
independently be using the same session number.
Your WiFi DSL modem router then sends this request message through the Internet to 
the web server at www.example.com.
4. The web server at www.example.com composes a return message with the requested web 
page data. The return message contains the following address and port information. The 
web server then sends this reply message to your WiFi DSL modem router.
•Source address. The IP address of www.example.com.
•Source port number. 80, which is the standard port number for a web server 
process.
•Destination address. The public IP address of your WiFi DSL modem router.
•Destination port number. 33333.
5. Upon receiving the incoming message, your WiFi DSL modem router checks its session 
table to determine whether an active session for port number 33333 exists. Finding an active 
session, the WiFi DSL modem router then modifies the message to restore the original  
						

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address information replaced by NAT. Your WiFi DSL modem router sends this reply 
message to your computer, which displays the web page from www.example.com. The 
message now contains the following address and port information:
•Source address. The IP address of www.example.com.
•Source port number. 80, which is the standard port number for a web server 
process.
•Destination address. Your computer’s IP address.
•Destination port number. 5678, which is the browser session that made the initial 
request.
6. When you finish your browser session, your WiFi DSL modem router eventually detects a 
period of inactivity in the communications. Your WiFi DSL modem router then removes the 
session information from its session table, and incoming traffic is no longer accepted on port 
number 33333.
Port Triggering to Open Incoming Ports
In the preceding example, requests are sent to a remote computer by your WiFi DSL modem 
router from a particular service port number, and replies from the remote computer to your 
WiFi DSL modem router are directed to that port number. If the remote server sends a reply 
to a different port number, your WiFi DSL modem router does not recognize it and discards it. 
However, some application servers (such as FTP and IRC servers) send replies to multiple 
port numbers. Using the port triggering function of your WiFi DSL modem router, you can tell 
the WiFi DSL modem router to open more 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 WiFi DSL 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 WiFi DSL modem router.
3. Your WiFi DSL modem router creates an entry in its internal session table describing this 
communication session between your computer and the IRC server. Your WiFi DSL 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 WiFi DSL 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 WiFi DSL modem router using the 
NAT-assigned source port (as in the previous example, say port 33333) as the destination  
						

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port. The IRC server also sends an identify message to your WiFi DSL modem router with 
destination port 113.
6. Upon receiving the incoming message to destination port 33333, your WiFi DSL modem 
router checks its session table to determine whether an active session for port number 
33333 exists. Finding an active session, the WiFi DSL 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 WiFi DSL modem 
router checks its session table and learns that an active session exists for port 113 
associated with your computer. The WiFi DSL 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 WiFi DSL modem router eventually senses a 
period of inactivity in the communications. The WiFi DSL 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.
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 WiFi 
DSL 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 WiFi DSL 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 WiFi DSL 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 WiFi DSL modem router.
•Destination port number. 80, which is the standard port number for a web server 
process. 
						

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The remote computer then sends this request message through the Internet to your WiFi 
DSL modem router.
2. Your WiFi DSL 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 WiFi DSL modem router modifies the destination information in the request 
message:
The destination address is replaced with 192.168.1.123.
Your WiFi DSL 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 
WiFi DSL modem router.
4. Your WiFi DSL 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.
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 require 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 WiFi DSL modem router to 
forward specific incoming protocols to computers on your local network. In addition to servers  
						

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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, applicatio\
n, or game you want 
to provide, and the local IP address of the computer that provides the s\
ervice. 

The server 
computer has to always have the same IP address.
Tip:T
o ensure that your server computer always has the same IP 
address, use the reserved IP address feature of your WiFi DSL 
modem router. 
To set up port forwarding:
1. Select  ADV
 ANCED > Advanced Setup > Port Forwarding/Port Triggering .
Port Forwarding is selected as the service type. 
						

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D6200 WiFi DSL Modem Router 
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 6.
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.
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. 
						

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 D6200 WiFi DSL Modem Router
3. 
Click the  Add Custom Service.
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.
Application Example: Making a Local Web Server Public
If you host a web server on your local network, you can use port forward\
ing 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 WiFi DSL modem router always gives your web server\
 an IP 
address of 192.168.1.33.  
						

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118 D6200 WiFi DSL Modem Router 
2. In the Port Forwarding/Port Triggering screen, configure the WiFi DSL 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 WiFi DSL 
modem router to use the name. 
For more information, see Dynamic DNS on page 120.
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 WiFi DSL modem router monitors outbound traffic 
looking for a specified outbound “trigger” port. When the WiFi DSL modem router detects 
outbound traffic on that port, it remembers the IP address of the local computer that sent the 
data. The WiFi DSL 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), you should also enable 
Universal Plug and Play (UPnP). For more information, see 
Universal 
Plug and Play on page 126.
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. Select ADVANCED > Advanced Setup > Port Forwarding/Port Triggering. 
						

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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 triggeri\
ng 
configuration information you added to the WiFi DSL 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 WiFi 
DSL modem router cannot be sure when the application has terminated.
5.  Click  Add Service. 
						

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6. In the Service Name field, type a descriptive service name. 
7. In the Service User list, select Any (the default).
This service can 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 open. 
10. Enter the inbound connection port information in the Connection 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 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 WiFi DSL modem router contains a client that can connect to the Dynamic DNS service 
provided by DynDNS.org. First visit their website at http://www.dyndns.org and obtain an 
account and host name that you configure in the WiFi DSL modem router. Then, whenever 
your ISP-assigned IP address changes, your WiFi DSL 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 WiFi DSL modem 
router at http://hostname.dyndns.org.