Dear All,
I have studied that the server will listen in well known port
numbers and the client will send request to that port and later the
communication will be handles by ephimeral ports by both ends by
forking a child in the server side. But if i sniff packets in
ethereal, why its showing the communication handles by the same well
known port number. If it happens like this, how can it handle
multiple client at the same time. Please clear me this confusion.

halidumar

Halid Umar A M wrote:
> Dear All,
> I have studied that the server will listen in well known port
> numbers and the client will send request to that port and later the
> communication will be handles by ephimeral ports by both ends by
> forking a child in the server side.


Some servers work like that, certainly not all.


> But if i sniff packets in
> ethereal, why its showing the communication handles by the same well
> known port number. If it happens like this, how can it handle
> multiple client at the same time. Please clear me this confusion.


A TCP session is identified by *four* parameters, source and
destination IP addresses, and source and destination ports (and
obviously source and destination switch depending on which direction a
packet is going). So long as at least one of those four items is
different, two sessions are distinct.

UDP doesn't have sessions in the same sense TCP does, but the way most
UDP servers operate you get basically the same effect.

In article <1148099588.076651.41700@j73g2000cwa.googlegroups. com>,
"robertwessel2@yahoo.com" <robertwessel2@yahoo.com> wrote:

> Halid Umar A M wrote:
> > Dear All,
> > I have studied that the server will listen in well known port
> > numbers and the client will send request to that port and later the
> > communication will be handles by ephimeral ports by both ends by
> > forking a child in the server side.
>
>
> Some servers work like that, certainly not all.
>
>
> > But if i sniff packets in
> > ethereal, why its showing the communication handles by the same well
> > known port number. If it happens like this, how can it handle
> > multiple client at the same time. Please clear me this confusion.
>
>
> A TCP session is identified by *four* parameters, source and
> destination IP addresses, and source and destination ports (and
> obviously source and destination switch depending on which direction a
> packet is going). So long as at least one of those four items is
> different, two sessions are distinct.

To expand on this, in most cases the source port used by the client will
be an ephemeral port, using the server's well known port as the
destination. Then the reply has the server's port as the source and the
client's ephemeral port as the destination.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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