TCP SYN packet Generation

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This topic contains 1 reply, has 2 voices, and was last updated by  Vadim Smirnov 10 years ago.

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  • #5157

    samj.magenic
    Participant

    I am creating a new TCP SYN packet, and sending it to the network card. All this workds perfectly well, except the SYN-ACK from the remote host is being rejected by the OS (it’s sending an RST automatically). My assumption is that the local port # I am assigning is not known to the OS and the OS is not expecting traffic on the specified port.

    My question then, is, using the WinPkFilter system, how do I query for or allocate a local (source) ethereal port number for use in creating my TCP connections in this fashion?


    Sa,

    #6510

    Vadim Smirnov
    Moderator

    System (TCPIP.SYS) recognizes SYN-ACK only when it was establishing the connection (sending SYN) itself. To force TCPIP.SYS to accept SYN-ACK you would have to modify TCPIP.SYS internal structures.

    Normally if you are trying to establish TCP connection with WinpkFilter you have to process SYN-ACK yourself without passing it up to TCPIP.SYS and generate ACK to complete the handshaking.

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