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6.

In the

Destination IP Address

field, enter the IP address of the final destination.

7.

In the

IP Subnet Mask

field, enter the IP subnet mask for this destination.

If the destination is a single host, enter

255.255.255.255

.

8.

In the

Gateway

IP Address

field, enter the gateway IP address, which must be a router on the

same LAN segment as the WNR2000 router.

9.

In the

Metric

field, enter a number between 1 and 15 as the metric value.

This represents the number of routers between your network and the destination. Usually, a

setting of 2 or 3 works, but if this is a direct connection, set it to 1.

10.

Click

Apply

to have the static route entered into the table.

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Chapter 5

Fine-Tuning Your Network

This chapter describes how to modify the configuration of the Wireless-N Router Model

WNR2000 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:

•

“Allowing Inbound Connections to Your Network

”

•

“Configuring Port Forwarding to Local Servers” on page 5-6

•

“Configuring Port Triggering” on page 5-9

•

“Using Universal Plug and Play” on page 5-13

•

“Optimizing Wireless Performance” on page 5-14

•

“Changing the MTU Size” on page 5-15

•

“Overview of Home and Small Office Networking Technologies” on page 5-17

Allowing Inbound Connections to Your Network

By default, the WNR2000 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

.

Your

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.