N150 4-Port Wireless Router JNR1010
Remote Computer Access Basics
When a computer on your network needs to access a computer on the Internet, your computer sends your router a message containing the source and destination address and process information. Before forwarding your message to the remote computer, your router must modify the source information and create and track the communication session so that replies can be routed back to your computer.
Following an example of normal outbound traffic and the resulting inbound responses:
1.You open a browser, and your operating system assigns port number 5678 to this browser session.
2.You type http://www.example.com into the URL field, and your computer creates a web page request message with the following address and port information:
•Source address. Your computer’s IP address.
•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.
The request message is sent to your router.
3.Your router creates an entry in its internal session table describing this communication session between your computer and the web server at www.example.com. Before sending the web page request message to www.example.com, your router stores the original information and then modifies the source information in the request message, performing Network Address Translation (NAT):
•The source address is replaced with your router’s public IP address. This step is necessary because your computer uses a private IP address that is not globally unique and cannot be used on the Internet.
•The source port number is changed to a number assigned by the router, such as 33333. This step is necessary because two computers could independently be using the same session number.
Your router then sends this request message through the Internet to the web server at www.example.com.
4.The web server at www.example.com composes a return message with the requested web page data. The return message contains the following address and port information. 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. The public IP address of your router.
•Destination port number. 33333.
The web server then sends this reply message to your router.
5.Upon receiving the incoming message, your router checks its session table to determine whether there is an active session for port number 33333. Finding an active session, the
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