NETGEAR wndr3700 - Manual (Page 86)

RangeMax™ Dual Band Wireless-N Gigabit Router WNDR3700 User Manual
Customizing Your Network Settings 5-14
v1.3, October 2009
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.
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:
Note: Only one computer at a time can use the triggered application.