Port Triggering To Open Incoming Ports - NETGEAR WNDR3700v4 User Manual

N600 Wireless Dual Band Gigabit Router WNDR3700v4
Source address. The IP address of www.example.com.
Source port number. 80, which is the standard port number for a web server process.
Destination address. Your computer's IP address.
Destination port number. 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
6.
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. Replies from the remote computer to your router are directed
to that port number. If the remote server sends a reply 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 to multiple port numbers. Using the port triggering function of your
router, you can tell the 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 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.
1.
Your IRC client composes a request message to an IRC server using a destination port
2.
number of 6667, the standard port number for an IRC server process. Your computer
then sends this request message to your router.
Your router creates an entry in its internal session table describing this communication
3.
session between your computer and the IRC server. Your 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
4.
6667, your 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 router using the NAT-assigned source
5.
port (as in the previous example, say port 33333) as the destination port. The IRC
server also sends an "identify" message to your router with destination port 113.
Upon receiving the incoming message to destination port 33333, your router checks its
6.
session table to determine whether there is an active session for port number 33333.
Finding an active session, the router restores the original address information replaced
by NAT and sends this reply message to your computer.
Advanced Settings
81