Control Access to the Internet
37
VDSL Voice Gateway
3.
(Optional) Register a host name with a Dynamic DNS service and specify that name in the
Dynamic DNS screen of the gateway.
For more information, see
70.
Dynamic DNS makes it much easier to access a server from the Internet because you
can type the name in the Internet browser. Otherwise, you must know the IP address that
the Internet service provider assigned, which typically changes.
How the Gateway Implements the Port Forwarding Rule
The following sequence shows the effects of a port forwarding rule:
1.
When you type the URL www.example.com in your browser, the browser sends 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 gateway.
•
Destination port number
. 80, which is the standard port number for a web server
process.
2.
Your gateway receives the message and finds your port forwarding rule for incoming port 80
traffic.
3.
The gateway changes the destination in the message to IP address 10.0.0.223 and sends
the message to that computer.
4.
Your web server at IP address 10.0.0.223 receives the request and sends a reply message
to your gateway.
5.
Your gateway performs Network Address Translation (NAT) on the source IP address and
sends the reply through the Internet to the computer or wireless device that sent the web
page request.
Port Triggering
Port triggering is a dynamic extension of port forwarding that is useful in these cases:
•
An application uses port forwarding to more than one local computer (but not
simultaneously).
•
An application opens incoming ports that are different from the outgoing port.
With port triggering, the gateway monitors traffic to the Internet from an outbound “trigger”
port that you specify. For outbound traffic from that port, the gateway saves the IP address of
the computer that sent the traffic. The gateway temporarily opens the incoming port or ports
that you specify in your rule, and forwards that incoming traffic to that destination.
Port forwarding creates a static mapping of a port number or range of ports to a single local
computer. Port triggering can dynamically open ports to any computer when needed and
close the ports when they are no longer needed.
