Port Forwarding And Port Triggering; Remote Computer Access Basics - NETGEAR CG3300CMR User Manual

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Port Forwarding and Port Triggering

By default, the gateway blocks inbound traffic from the Internet to your computers except for
replies to your outbound traffic. Create exceptions to this rule for these purposes:
To allow remote computers on the Internet to access a server on your local network.
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To allow certain applications and games to work correctly when your gateway does not
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recognize their replies.
Your gateway provides two features for creating these exceptions: port forwarding and port
triggering. The next sections provide background information to help you understand how
port forwarding and port triggering work, and the differences between the two.

Remote Computer Access Basics

When a computer on your network accesses a computer on the Internet, your computer
sends your gateway a message containing the source and destination address and process
information. Before forwarding your message to the remote computer, your gateway has to
modify the source information and create and track the communication session so that
replies can be routed back to your computer.
Here is an example of normal outbound traffic and the resulting inbound responses:
You open a browser, and your operating system assigns port number 5678 to this
1.
browser session.
You type http://www.example.com into the URL field, and your computer creates a web page
2.
request message with the following address and port information. The request message is
sent to your gateway.
Source address. The IP address of your computer.
Source port number. 5678, which is the browser session.
Destination address. The IP address of www.example.com, which your computer finds
by asking a DNS server.
Destination port number. 80, which is the standard port number for a web server
process.
Your gateway creates an entry in its internal session table describing this communication
3.
session between your computer and the web server at www.example.com. Before sending
the web page request message to www.example.com, your gateway stores the original
information and then modifies the source information in the request message, performing
Network Address Translation (NAT):
Wireless Cable Gateway CG3300CMR
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