Netgear D6300 사용자 설명서

Destination port number. 5678, which is the browser session that made the initial 
request.

When you finish your browser session, your WiFi modem router eventually detects a period 

of inactivity in the communications. Your WiFi modem 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 WiFi modem 
router from a particular service port number, and replies from the remote computer to your 
WiFi modem router are directed to that port number. If the remote server sends a reply to a 
different port number, your WiFi modem router does not recognize it and discards it. 
However, some application servers (such as FTP and IRC servers) send replies to multiple 
port numbers. Using the port triggering function of your WiFi modem router, you can tell the 
WiFi modem router to open additional incoming ports when a particular outgoing port 
originates a session.

An example is Internet Relay Chat (IRC). Your computer connects to an IRC server at 
destination port 6667. The IRC server not only responds to your originating source port, but 
also sends an “identify” message to your computer on port 113. Using port triggering, you can 
tell the WiFi modem router, “When you initiate a session with destination port 6667, you have 
to also allow incoming traffic on port 113 to reach the originating computer.” Using steps 
similar to the preceding example, the following sequence shows the effects of the port 
triggering rule you have defined:

You open an IRC client program to start a chat session on your computer. 

Your IRC client composes a request message to an IRC server using a destination port 

number of 6667, the standard port number for an IRC server process. Your computer then 

sends this request message to your WiFi modem router.

Your WiFi modem router creates an entry in its internal session table describing this 

communication session between your computer and the IRC server. Your WiFi modem 

router stores the original information, performs Network Address Translation (NAT) on the 

source address and port, and sends this request message through the Internet to the IRC 

server. 

Noting your port triggering rule and having observed the destination port number of 6667, 

your WiFi modem router creates an additional session entry to send any incoming port 113 

traffic to your computer.

The IRC server sends a return message to your WiFi modem router using the 

NAT-assigned source port (as in the previous example, say port 33333) as the destination 

port. The IRC server also sends an identify message to your WiFi modem router with 

destination port 113.

Upon receiving the incoming message to destination port 33333, your WiFi modem router 

checks its session table to determine whether there is an active session for port number 

33333. Finding an active session, the WiFi modem router restores the original address 

information replaced by NAT and sends this reply message to your computer.