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uniquely identifies every interhost connection in the network. While many processes may be talking to the process that handles remote login requests (therefore their packets have the same destination IP addresses and port numbers), they will have unique pairs of source IP addresses and port numbers. The destination port number determines which of the many processes using TCP or UDP gets the data. On most Unix systems port numbers below 1024 are reserved for the processes executing with superuser privileges, while ports 1024 and above may be used by any user. This enforces some measure of security by preventing random user applications from accessing ports used by servers. However, given that most nodes on the network don't run Unix, this measure of security is very questionable.source IP address, source port, destination IP address, destination port
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1.3. Network layer | ![]() | 1.5. The session and presentation layers |
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