While the port selection is random it does effectively make sure something isn't
already
bound to that port and if it is it will select another random port until it finds a
free
port.
Darren
Chuck Larrieu wrote:
> Got a question about this.
>
> Application wants to open a TCP connection to something - say http, so the
> application issues the request, TCP on the application side uses some random
> port number above 1023 as the source port number. The destination port is
> the well know port on the distant end.
>
> However, I see from the IANA port listings
> (http://www.isi.edu/in-notes/iana/assignments/port-numbers ) that there are
> any number of registered ports above 1023. For example L2TP uses port 1701,
> Groupwise uses port 1677, ands WINS uses port 1512. The IANA page itself
> calls ports 1024 through 49151 "registered" and further states that only
> ports 49152 and beyond are "dynamic and / or private"
>
> Anyone ever sniffed outbound traffic and seen apps using source ports in the
> 1024 through 49151 range?
>
> It just occurs to me that this has the potential of creating problems, if an
> application uses a port reserved for some other application. Since most of
> the ports in this "registered" range appear to be for obscure kinds of
> services or applications, perhaps this isn't really and issue.
>
> Comments?
>
> Chuck
>
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