well known and ephimeral port numbers - TCP-IP

This is a discussion on well known and ephimeral port numbers - TCP-IP ; 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 ...

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Thread: well known and ephimeral port numbers

  1. well known and ephimeral port numbers

    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


  2. Re: well known and ephimeral port numbers


    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.


  3. Re: well known and ephimeral port numbers

    In article <1148099588.076651.41700@j73g2000cwa.googlegroups.c om>,
    "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
    *** PLEASE post questions in newsgroups, not directly to me ***
    *** PLEASE don't copy me on replies, I'll read them in the group ***

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