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N150 Wireless ADSL2+ Modem Router DGN1000Bv3
The following sequence shows the effects of the port forwarding rule you have defined:
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 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 modem router
• Destination 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
modem router.
2. Your modem router receives the request message and looks in its rules table for any rules
covering the disposition of incoming port 80 traf
fic. Your port forwarding rule specifies that
incoming port 80 traffic needs to be forwarded to local IP address 192.168.0.123. Therefore,
your modem router modifies the destination information in the request message:
The destination address is replaced with 192.168.0.123.
Your modem router then sends this request message to your local network.
3. Your web server at 192.168.0.123 receives the request and composes a return message
with the requested web page data.
Your web server then sends this reply message to your
modem router.
4. Your 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 must know which inbound ports the application needs. You
usually can determine this information by contacting the publisher of the application or the
relevant user groups or news groups.
How Port Forwarding Differs from Port Triggering
The following points summarize the differences between port forwarding and port triggering:
• Any computer on your network can use port triggering, although only one computer can
use it at a time.
• Port forwarding is configured for a single computer on your network.
• With port triggering, the modem router does not need to 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 triggering requires specific outbound traffic to open the inbound ports, and the
triggered ports are closed after a period of no activity
.
• Port forwarding is always active and does not need to be triggered.