source ports

Unanswered Question
Feb 6th, 2008

Hi all, when pc's / servers make sessions to other pc's and servers etc, do they just pick a random port between a certain range, also when would the source port be the same as the destination port? would tftp be a good example , would it use port 69 from source to dest ?

I have this problem too.
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c.lemaire Wed, 02/06/2008 - 01:41

Hi,

In most TCP/IP client/server communications, the client uses a random ephemeral port number but the algorithm used to select that port is OS dependent.

For UDP, lots of protocols use the same source port as the destination port but it is not mandatory. SNMP and NTP usually do so while TFTP usually doesn't...

s.arunkumar Wed, 02/06/2008 - 01:45

Hi

To add Let me give the range of port

Well know - 1 - 1024

Reserve - 1024 - 49151

private - 49152-65535

Now the port number for source and destination depends on application or protocols.

Say for http ,the host will take a random port number from private range given above and the destination would be 80.

There are applications that uses same port number..

arun

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