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Page 81 / 149 Scroll up to view Page 76 - 80
RangeMax™ Dual Band Wireless-N Gigabit Router WNDR3700 User Manual
Customizing Your Network Settings
5-9
v1.3, October 2009
3.
Click
Apply
.
Configuring Static Routes
Static routes provide additional routing information to your router. Under usual circumstances, the
router has adequate routing information after it has been configured for Internet access, and you do
not need to configure additional static routes. You must configure static routes only for unusual
cases such as multiple routers or multiple IP subnets located on your network.
As an example of when a static route is needed, consider the following case:
•
Your primary Internet access is through a cable modem to an ISP.
•
You have an ISDN router on your home network for connecting to the company where you are
employed. This router’s address on your LAN is
1
92.168.1.100.
•
Your company’s network address is 134.177.0.0.
When you first configured your router, two implicit static 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 this configuration, if you attempt to access a device on the
134.177.0.0 network, your 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 must define a static route, telling your router that 134.177.0.0 should be accessed
through the ISDN 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 router at 192.168.1.100.
•
A
Metric
value of 1 will work since the ISDN router is on the LAN.
•
Private
is selected only as a precautionary security measure in case RIP is activated.
Page 82 / 149
RangeMax™ Dual Band Wireless-N Gigabit Router WNDR3700 User Manual
Customizing Your Network Settings
5-10
v1.3, October 2009
Select
Static Routes
under Advanced in the main menu. The Static Routes screen displays.
To add or edit a static route:
1.
Click
Add
to open the Static Routes screen.
2.
In the
Route Name
field, type a name for this static route. (This is for identification purposes
only.)
3.
Select the
Private
check box if you want to limit access to the LAN only. If Private is selected,
the static route is not reported in RIP.
4.
Select the
Active
check box to make this route effective.
5.
Type the destination IP address of the final destination.
6.
Type the IP subnet mask for this destination.
If the destination is a single host, type 255.255.255.255.
7.
Type the gateway IP address, which must be a router on the same LAN segment as the
WNDR3700 router.
Figure 5-4
Figure 5-5
Page 83 / 149
RangeMax™ Dual Band Wireless-N Gigabit Router WNDR3700 User Manual
Customizing Your Network Settings
5-11
v1.3, October 2009
8.
Type 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.
9.
Click
Apply
to have the static route entered into the table.
Allowing Inbound Connections to Your Network
By default, the WNDR3700 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.
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.
Page 84 / 149
RangeMax™ Dual Band Wireless-N Gigabit Router WNDR3700 User Manual
Customizing Your Network Settings
5-12
v1.3, October 2009
•
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.
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.
Page 85 / 149
RangeMax™ Dual Band Wireless-N Gigabit Router WNDR3700 User Manual
Customizing Your Network Settings
5-13
v1.3, October 2009
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,
“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.

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