Port Triggering To Open Incoming Ports - NETGEAR C6300BD User Manual

AC1900, N900, and N450 WiFi Cable Data Gateways
• Destination port number. 5678, which is the browser session that made the initial
request
6. When you finish your browser session, your cable data gateway eventually detects a period
of inactivity in the communications and removes the session information from its session
table. Incoming traffic is no longer accepted on port number 33333.

Port Triggering to Open Incoming Ports

Some application servers (such as FTP and IRC servers) send replies to multiple port
numbers. Using the port triggering function of your cable data gateway, you can tell the cable
data gateway to open more 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 cable data gateway, "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 this port triggering rule:
1. You open an IRC client program to start a chat session on your computer.
2. 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 cable data gateway.
3. Your cable data gateway creates an entry in its internal session table describing this
communication session between your computer and the IRC server. Your cable data
gateway 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.
4. When the cable data gateway detects the port triggering rule and the destination port
number of 6667, it creates an additional session entry to send any incoming port 113 traffic
to your computer.
5. The IRC server sends a return message to your cable data gateway using the
NAT-assigned source port (for example, port 33333) as the destination port and sends an
"identify" message to your cable data gateway with destination port 113.
6. When your cable data gateway detects the incoming message to destination port 33333, it
checks its session table for an active session for port number 33333. Finding an active
session, the cable data gateway restores the original address information replaced by NAT
and sends this reply message to your computer.
7. When your cable data gateway detects the incoming message to destination port 113, it
checks its session table and learns that an active session for port 113 is associated with
your computer. The cable data gateway replaces the message's destination IP address
with your computer's IP address and forwards the message to your computer.
8. When you finish your chat session, your cable data gateway eventually detects a period of
inactivity in the communications. The cable data gateway then removes the session
information from its session table and incoming traffic is no longer accepted on port numbers
33333 or 113.
Configure Advanced Features
119