Netgear Router WGR614v8 User Manual

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Chapter 5
Fine-Tuning Your Network
This chapter describes how to modify the configuration of the Wireless-G Router Model 
WGR614v8 to allow specific applications to access the Internet or to be accessed from the 
Internet, and how to make adjustments to enhance your network’s performance.
This chapter includes the following sections:
•““Changing the MTU Size” on page 5-20”
•“Configuring Port Forwarding to Local Servers” on page 5-6
•“Configuring Port Triggering” on page 5-9
•“Using Universal Plug and Play” on page 5-12
•“Optimizing Wireless Performance” on page 5-13
•“Configuring Quality of Service” on page 5-14
•“Changing the MTU Size” on page 5-20
•“Overview of Home and Small Office Networking Technologies” on page 5-22
Allowing Inbound Connections to Your Network
By default, the Wireless-G Router blocks any inbound traffic from the Internet to your computers 
except for replies to your outbound traffic. However, you might need to create exceptions to this 
rule for the following purposes:
• To allow remote computers on the Internet to access a server on your local network. 
• To allow certain applications and games to work correctly when their replies are not 
recognized by your router.
Your router provides two features for creating these exceptions: port forwarding and port 
triggering. This section explains how a normal outbound connection works, followed by two 
examples explaining how port forwarding and port triggering operate and how they differ. 
						

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How Your Computer Accesses a Remote Computer through Your 
Router
When a computer on your network needs to access a computer on the Internet, your computer 
sends your router a message containing source and destination address and process information. 
Before forwarding your message to the remote computer, your router must modify the source 
information and must 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 Internet Explorer, beginning a browser session on your computer. Invisible to you, 
your operating system assigns a service number (port number) to every communication 
process running on your computer. In this example, let’s say Windows assigns port number 
5678 to this browser session. 
2. You ask your browser to get a Web page from the Web server at www.example.com. Yo u r  
computer composes a Web page request message with the following address and
port information: 
• The source address is your computer’s IP address.
• The source port number is 5678, the browser session. 
• The destination address is the IP address of www.example.com, which your computer 
finds by asking a DNS server.
• The destination port number is 80, the standard port number for a Web 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 Web server at www.example.com. Before sending the Web 
page request message to www.example.com, your 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 router’s public IP address.
This 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 router, such as 33333. This 
is necessary because two computers could independently be using the same session 
number.
Your router then sends this request message through the Internet to the Web server at 
www.example.com. 
						

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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 source address is the IP address of www.example.com.
• The source port number is 80, the standard port number for a Web server process.
• The destination address is the public IP address of your router.
• The destination port number is 33333.
The Web server then sends this reply message to your router.
5. Upon receiving the incoming message, your router checks its session table to determine 
whether there is an active session for port number 33333. Finding an active session, the router 
then modifies the message, restoring the original address information replaced by NAT. The 
message now contains the following address and port information: 
• The source address is the IP address of www.example.com.
• The source port number is 80, the standard port number for a Web server process.
• The destination address is your computer’s IP address.
• The destination port number is 5678, the browser session that made the initial request.
Your router then sends this reply message to your computer, which displays the Web page 
from www.example.com.
6. When you finish your browser session, your router eventually senses a period of inactivity in 
the communications. Your router then removes the session information from its session table, 
and incoming traffic is no longer accepted on port number 33333.
How Port Triggering Changes the Communication Process
In the preceding example, requests are sent to a remote computer by your router from a particular 
service port number, and replies from the remote computer to your router are directed to that port 
number. If the remote server sends a reply back to a different port number, your router will not 
recognize it and will discard it. However, some application servers (such as FTP and IRC servers) 
send replies back to multiple port numbers. Using the port triggering function of your router, you 
can tell the 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 router,  
						

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“When you initiate a session with destination port 6667, you must 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, beginning 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 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 (as 
in the previous example, let’s say 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 
user groups or newsgroups.
Note: Only one computer at a time can use the triggered application. 
						

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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 4-6.
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 Wireless-G Router. See “Using Address 
Reservation” on page 4-3 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.
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 box, enter the last digit of the IP address of your local 
computer that will provide this service. 
4.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 Custom Service.
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 Star ting  Po rt 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:
1.In the table, select the 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. 
Figure 5-2 
						

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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 4-3. 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 4-4. 
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.
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. 
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) according 
to the instructions in “Using Universal Plug and Play” on page 5-12. 
						

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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 
user groups or newsgroups.
To set up port triggering: 
1.Select Port Forwarding/Port Triggering under Advanced in the main menu. The 
Forwarding/Port Triggering screen displays.
2.Select the Port Triggering radio button. The port triggering information displays.
3.Clear the Disable Port Triggering check box.
Figure 5-3
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 router is retained even though it is 
not used.