Netgear WNDR3800 사용자 설명서

the Web page request message to www.example.com, your router stores the original 

information and then modifies the source information in the request message, performing 

Network Address Translation (NAT):

The source address is replaced with your router’s public IP address. This is necessary 

because your computer uses a private IP address that is not globally unique and 
cannot be used on the Internet.

The source port number is changed to a number chosen by the router, such as 33333. 

This is necessary because two computers could independently be using the same 
session number.

Your router then sends this request message through the Internet to the Web server at 
www.example.com.

The Web server at www.example.com composes a return message with the requested Web 

page data. The return message contains the following address and port information. The 

Web server then sends this reply message to your router.

. The IP address of www.example.com.

. 80, which is the standard port number for a Web server process.

. The public IP address of your router.

. 33333.

Upon receiving the incoming message, your router checks its session table to determine 

whether there is an active session for port number 33333. Finding an active session, the 

router then modifies the message to restore the original address information replaced by 

NAT. Your router sends this reply message to your computer, which displays the Web 

page from www.example.com. The message now contains the following address and port 

information.

. The IP address of www.example.com.

. 80, which is the standard port number for a Web server process.

. Your computer’s IP address.

. 5678, which is the browser session that made the initial 

request.

When you finish your browser session, your router eventually detects a period of inactivity in 

the communications. Your router then removes the session information from its session 

table and incoming traffic is no longer accepted on port number 33333.

Port Triggering to Open Incoming Ports

In the preceding example, requests are sent to a remote computer by your router from a 
particular service port number, and replies from the remote computer to your router are 
directed to that port number. If the remote server sends a reply back to a different port 
number, your router does not recognize it and discards it. However, some application servers 
(such as FTP and IRC servers) send replies back to multiple port numbers. Using the port