accept() return point vs incoming SYN - Networking

This is a discussion on accept() return point vs incoming SYN - Networking ; 3-way handshake is (1) C->S SYN (2) C->S SYN (3) C->S ACK. The accept syscall returns at the point when packet #3 is received on server, correct ? Not when packet #1 is received. Is it same on all OSes ...

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Thread: accept() return point vs incoming SYN

  1. accept() return point vs incoming SYN

    3-way handshake is (1) C->S SYN (2) C->S SYN (3) C->S ACK.

    The accept syscall returns at the point when packet #3 is received on
    server,
    correct ? Not when packet #1 is received.

    Is it same on all OSes ? Are there OS where accept
    returns after packets No.1 is received by server ?

    Thanks
    V.M.

  2. Re: accept() return point vs incoming SYN

    viki writes:

    > 3-way handshake is (1) C->S SYN (2) C->S SYN (3) C->S ACK.



    Well, it's more like

    C->S SYN
    S->C SYN & ACK
    C->S ACK


  3. Re: accept() return point vs incoming SYN

    viki wrote:
    > 3-way handshake is (1) C->S SYN (2) C->S SYN (3) C->S ACK.


    > The accept syscall returns at the point when packet #3 is received
    > on server, correct ? Not when packet #1 is received.


    > Is it same on all OSes ? Are there OS where accept
    > returns after packets No.1 is received by server ?


    There is at least one OS where accept() can return after the SYN is
    received, although it still employs a SYN flood defense:

    HP-UX tardy B.11.11 U 9000/785 2002119164 unlimited-user license
    $ ndd -h tcp_early_conn_ind

    tcp_early_conn_ind:

    If set to 1, a T_CONN_IND message is sent upstream as soon as a
    SYN packet is received from a remote host which is on the TCP's
    'good guy' list. A remote host goes on the 'good guy' list if it
    is known to have completed the 3-way handshake earlier.
    If set to 0, the T_CONN_IND message is not sent upstream until
    the 3-way handshake is complete, even if the remote host is
    on the 'good guy' list.
    [0,1] Default: 1

    What leads you to ask the question?

    rick jones
    --
    oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

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