Port Forwarding To Permit External Host Communications - NETGEAR D2200D-1FRNAS User Manual

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 gateway. The
remote computer composes a web page request message with the following destination
information:
Destination address. The IP address www.example.com, which is the gateway's address.
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
gateway.
2. Your gateway 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 gateway modifies the destination information in the request message:
The destination address is replaced with 192.168.1.123.
Your gateway then sends this request message to your local network.
3. Your 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 the gateway a reply
message.
4. Your gateway 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.

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 gateway 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 gateway, "When you receive incoming traffic on port 80 (the
standard port number for a web server process), forward it to the local computer at
192.168.1.123." 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 gateway. 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
gateway.
Destination port number. 80, which is the standard port number for a web server process.
ADSL2+ Gateway
DRAFT
Control Access to the Internet
23