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::Let's look at how these rules would apply to a simple web connection (HTTP - port 80):
::# For the ''request''(originating from browser on local machine), the '''source port (sport) for the example in the above diagram is 40112(browser on local machine)''' and the '''destination port (dport) is 80(webserver on remote machine)'''::# For the ''response''(originating from server on remote machine), the '''source port (sport) is 80(webserver on remote machine)''' and the '''destination port (dport) is 40112(browser on local machine)'''
::# Since the '''RELATED,ESTABLISHED''' rule already exists, we are only concerned about <u>'''controlling'''</u> the '''incoming traffic on the server''', which in our example, the '''chain is: INPUT''', the '''protocol is: tcp''', and the '''destination is: port 80'''.