Netgear DC112A User's Guide download pdf (Page 57)

Control Internet Access

AirCard Smart Cradle

HTTP (port 80) is the standard protocol for web servers.

3. (Optional) Register a host name with a Dynamic DNS service and specify that name in the

Dynamic DNS screen of the cradle.

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 ISP assigned, which typically changes.

How the Cradle 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 cradle.

• Destination port number. 80, which is the standard port number for a web server

process.

2. Your cradle receives the message and finds your port forwarding rule for incoming port 80

traffic.

3. The cradle changes the destination in the message to IP address 192.168.100.123 and

sends the message to that computer.

4. Your web server at IP address 192.168.100.123 receives the request and sends a reply

message to your cradle.

5. Your cradle 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.

Set Up Port Triggering

Port triggering is a dynamic extension of port forwarding that is useful in these cases:

• An application must use port forwarding to more than one local computer (but not

simultaneously).

• An application must open incoming ports that are different from the outgoing port.

With port triggering, the cradle monitors traffic to the Internet from an outbound “trigger” port

that you specify. For outbound traffic from that port, the cradle saves the IP address of the

computer that sent the traffic. The cradle 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.

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Netgear DC112A User's Guide Page 57