Also,if two Netscape windows are both accessing different parts of the same web site, how does the Linux box running Netscape sort out the TCP packets coming back from the web server?
This is where the "source port" comes in: every new TCP connection gets a different source port, os everyone can tell them apart, even if they are going to the same destination IP address and the same destination port. Usually the first source port given will be 1024, and will increase over time.
"/etc/services"
