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Old 04-04-2009, 05:14 PM   #1
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Is it possible for two hosts to use the same source port ?


I was reading about data communication on the net and i got a little confused. There are 65535 available port numbers and the port numbers from 1-1024 are reserved for applications and such. That leaves 64511 ports available. My question is, when a web server has a number of connections from users which are larger than the amount of ports available, how can it handle more connections ? Every host that connects to the web server needs a source port, can several hosts share the same port numbers (and then the connections would be differentiated with the TCP ACK field and sequence numbers for example) ?

Thanks for all help.
Old 04-04-2009, 06:39 PM   #2
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A connection in the internet (a TCP connection) is always identified by two couples of numbers: (source address, source port), (destination address, destination port)
So, two different source addresses can have the same source port, as this results in two different connection identifiers.
A book about connections should absolutely explain this thing! If not, try complementing that book with some other source
Old 04-05-2009, 11:04 AM   #3
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If your webserver runs out of available ports to use for connections, it doesn't accept more until one becomes free. Typically this is called a Denial of Service (DoS).

Source ports are specific to the local machine. A single computer can't use the same source port for multiple applications at the same time, as the port would be already bound and reported as in-use to the OS. However, multiple computers connecting to the same destination could use the same source port.
Old 04-06-2009, 01:35 AM   #4
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thanks, great answers.


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