Netgear LG2200D User's Guide download pdf (Page 32)

Control Access to the Internet

U.S. Cellular® 4G LTE™ Router (LG2200D)

Port Forwarding to Permit External Host Communications

In both 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 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

relationship 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 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

192.168.0.123.”

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 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 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

router.

2. Your router receives the request message and looks in its rules table for any rules covering

the handling of incoming port 80 traffic. Your port forwarding rule specifies that incoming port

80 traffic should be forwarded to local IP address 192.168.0.123. Therefore, your router

modifies the destination information in the request message:

The destination address is replaced with 192.168.0.123.

Your 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

router.

4. Your 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 inbound ports the application needs.

You can usually find this information by contacting the publisher of the application or the

relevant user groups or news groups.

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Netgear LG2200D User's Guide Page 32