Port Forwarding To Permit External Host Communications - NETGEAR AC1200 JR6100 User Manual

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 router.
3. Your router creates an entry in its internal session table describing this communication
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.
4. Noting your port triggering rule and having observed the destination port number of 6667,
your router 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 router using the NAT-assigned source port
(for example, port 33333) as the destination port. The IRC server also sends an "identify"
message to your router with destination port 113.
6. When your router receives 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
router restores the original address information replaced by NAT and sends this reply
message to your computer.
7. When your router receives the incoming message to destination port 113, it checks its
session table and finds an active session for port 113 associated with your computer. The
router 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 router eventually senses a period of inactivity in the
communications. The router then removes the session information from its session table,
and incoming traffic is no longer accepted on port numbers 33333 or 113.
To configure port triggering, you must know which inbound ports the application needs. Also,
you must know the number of the outbound port that will trigger the opening of the inbound
ports. You can usually find this information by contacting the publisher of the application or
the relevant user groups or news groups.
Only one computer at a time can use the triggered application.
Port Forwarding to Permit External Host
Communications
In the preceding example, your computer initiates an application session with a server
computer on the Internet. However, you might need to allow a client computer on the Internet
to initiate a connection to a server computer on your network. Normally, your router ignores
any inbound traffic that is not a response to your own outbound traffic. You can configure
exceptions to this default rule by using the port forwarding feature.
A typical application of port forwarding can be shown by reversing the client-server
relationship from the previous web server example. In this case, a remote computer's
browser needs to access a web server running on a computer in your local network. Using
port forwarding, you can tell the router, "When you receive incoming traffic on port 80 (the
standard port number for a web server process), forward it to the local computer at
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