Advanced Settings
105
D6300 WiFi DSL Modem Router
7. Upon receiving the incoming message to destination port 113, your WiFi modem router
checks its session table and learns that there is an active session for port 113 associated
with your computer. The WiFi 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 f
inish your chat session, your WiFi modem router eventually senses a period of
inactivity in the communications. The WiFi 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 n
eed 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
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
re
lationship 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 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. T
he 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 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 modem router.
Destination port number. 8
0, which is the standard port number for a web server
process.
The remote computer then sends this request message through the Internet to your WiFi
modem rout
er.
2. Y
our WiFi 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.
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