Dynamic port use

[Mayank Jain Nawal]

On Wednesday 14 May 2008 9:30:01 pm devel-request at pidgin.im wrote:
> Mayank Jain Nawal spake unto us the following wisdom:
> > At most of the places chatting is not allowed, to stop users from doing
> > that port numbers are generally blocked. So are we still using port
> > numbers for identifying that the traffic belong to specific application
> > (I guess in pidgin we are are using port numbers).
>
> What are you trying to say?  This email does not make sense.
I mean why user need to specify which port his application is using? What is 
the need to specify the Connection port number. 
>
> Pidgin uses a random local port, and for every protocol the remote
> port is configurable.  However, servers only listen on particular
> ports.  For some (such as AOL's OSCAR servers) any port can be used,
> for others (most XMPP servers) only a very specific port can be used.
> There is nothing the client can do about this.
>
> > Possible solution to this is use of Dynamic ports. User should not be
> > restricted to use a particular port for certain application, the
> > identification of packet should be on the basis of certain unique string
> > or certain signature which should be present in every packet, not on the
> > basis of port which a particular application uses.
>
> I think you need to look into a decent networking textbook.  
> Packet 
> classification is handled by the operating system, not the
> application, and for TCP (which all IM protocols supported by Pidgin
> use for their primary negotiations) the port numbers of a connection
> are fixed from connection establishment forward.
>
> If my comments do not address your concerns, please try to clarify
> your concerns.  As I said, they do not really make sense.
>
> Ethan
>
> --
> The laws that forbid the carrying of arms are laws [that have no remedy
> for evils].  They disarm only those who are neither inclined nor
> determined to commit crimes.
>                 -- Cesare Beccaria, "On Crimes and Punishments", 1764

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Regards
Mayank Jain Nawal