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Specify Internet Port Settings
91
N600 WiFi Cable Modem Router Model C3700
5. Select the Port Triggering radio button.
6. Select a radio button to specify when you want to use port triggering:
• Never.
The modem router does not use port triggering even if you have specified port
triggering settings.
• Per Schedule. Port triggering is used based on the settings in the Schedule screen.
• Always.
Always use port triggering.
7. In the Port T
riggering Timeout field, enter a value up to 9999 minutes.
This value controls how long the inbound ports stay open when the modem router detects
no activity
. This value is required because the modem router cannot detect when the
application terminates.
Application Example: Port Triggering for Internet Relay Chat
Some application servers, such as FTP and IRC servers, send replies to multiple port
numbers. Using port triggering, you can tell the modem router to open more incoming ports
when a particular outgoing port starts 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 modem router, “When you initiate a session with destination port 6667, you must also
allow incoming traffic on port 113 to reach the originating computer.” The following sequence
shows the effects of the port triggering rule you have defined:
1. Y
ou open an IRC client program to start a chat session on your computer.
2. Y
our 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 modem router.
3. Y
our modem router creates an entry in its internal session table describing this
communication session between your computer and the IRC server. Your 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.
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