NETGEAR WNDR3700v4 User Manual page 80

N600 Wireless Dual Band Gigabit Router WNDR3700v4
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 router.
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.
Your router 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 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 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 chosen by the router, such as 33333.
•
This 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.
The web server at www.example.com composes a return message with the requested web
4.
page data. The return message contains the following address and port information. The
web server then sends this reply message to your router.
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.
Upon receiving the incoming message, your router checks its session table to determine
5.
whether there is an active session for port number 33333. Finding an active session, the
router then modifies the message to restore the original address information replaced by
NAT. Your router sends this reply message to your computer, which displays the web page
from www.example.com. The message now contains the following address and port
information.
Advanced Settings
80