Verizon 4G LTE User Manual page 62

Example: 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 enter a website address into the URL field, and your computer creates a web page
request message with the following information to your router.
• Source address: Your computer's IP address.
• Source port number: 5678, which is the browser session.
• Destination address: The website's IP address.
• 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. Before sending the web page request
message, 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 the public IP address of your router. 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 that the router chooses, 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.
4. The web server then composes a return message with the requested web page data to your
router. The return message contains the following information:
• Source address: The website's IP address.
• Source port number: 80, which is the standard port number for a web server
process.
• Destination address: Your router's public IP address router
• Destination port number: 33333.
5. Upon receiving the incoming message, your router checks its session table to determine
whether an active session for port number 33333 exists. If yes, the router then modifies the
message to restore the original address information that NAT replaced. Your router sends
this reply message to your computer, which shows the web page. The message now
contains the following information:
• Source address: The website's IP address.
• 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 no longer accepts incoming traffic on port number 33333.
Verizon 4G LTE Broadband Router
Advanced Router Settings
61