Netgear WNR2500 User Manual - Page 87

Source address, Source port number, Destination address, Destination port number

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N450 Wireless Router WNR2500 • 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. 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 replacement 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 change 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 web server then sends this reply message to your router. 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. 5. When your router receives the incoming message, it checks its session table for 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: • 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. Your computer's IP address. • Destination port number. 5678, which is the browser session that made the initial request. 6. When you finish your browser session, your router eventually detects a period of inactivity in the communications. Your router then removes the session information from its session table, and port number 33333 no longer accepts incoming traffic. Advanced Settings 87

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Advanced Settings
87
N450 Wireless Router WNR2500
•
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.
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
replacement 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 change 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 web server then sends this reply message to your router. 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.
5.
When your router receives the incoming message, it checks its session table for 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:
•
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
. Your computer’s IP address.
•
Destination port number
. 5678, which is the browser session that made the initial
request.
6.
When you finish your browser session, your router eventually detects a period of inactivity in
the communications. Your router then removes the session information from its session
table, and port number 33333 no longer accepts incoming traffic.