Netgear DGND4000 User Manual download pdf (Page 114)

Advanced Settings

114

N750 Wireless Dual Band Gigabit ADSL Modem Router DGND4000

Port Forwarding to Permit External Host Communications

In both of 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 wireless

modem 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 b

y 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 wireless modem 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 192.168.1.123.” The following sequence shows the effects of the port forwarding

rule you have defined:

1. The user of a re

mote computer opens a browser and requests a web page from

www.example.com, which resolves to the public IP address of your wireless 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

wireless modem router.

Destination port number. 80, which is th

e standard port number for a web server

process.

The remote computer then sends this request message through the Internet to your

wirel

ess modem router.

2. Y

our wireless modem router 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 wireless modem router modifies the destination information in the request

message:

The destination address is repla

ced with 192.168.1.123.

Your wireless modem router then sends this reque

st message to your local network.

3. Y

our 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 this reply message to your

wireless modem router.

4. Y

our wireless 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 need to know which inbou

nd ports the application needs.

Usually you can determine this information by contacting the publisher of the application or

the relevant user groups and newsgroups.

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