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D6200 WiFi DSL Modem Router
1. The 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 DSL modem
router. The remote computer composes a web page request message with the following
destination information:
• Destinati
on address. The IP address of www.example.com, which is the address of
your WiFi DSL modem router.
• Destinati
on port number. 80, 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
DS
L modem router.
2. Y
our WiFi DSL 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.
Therefore, your WiFi DSL modem router modifies the destination information in the request
message:
The destination address is repla
ced with 192.168.1.123.
Your WiFi DSL modem router then sends this reque
st message to your local network.
3. Y
our 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
WiFi DSL modem router.
4. Y
our WiFi DSL modem 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 inbou
nd ports the application needs.
Usually you can determine this information by contacting the publisher of the application or
the relevant user groups and newsgroups.
How Port Forwarding Differs from Port Triggering
The following points summarize the differences between port forwarding and port triggering:
• Port triggerin
g can be used by any computer on your network, although only one
computer can use it at a time.
• Port forward
ing is configured for a single computer on your network.
• Port triggering do
es not require that you 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 can never change.
• Port triggerin
g requires specific outbound traffic to open the inbound ports, and the
triggered ports are closed after a period of no activity.
• Port forward
ing is always active and does not need to be triggered.