Thread: packet analyzer in c

  1. #16
    Registered User
    Join Date
    Jul 2004
    I am still looking around for help. Thax alot for the good work from Sang-drax

    Now, I have :
    u_long SEQ_N // sequence # in a tcp header
    I need to extract that from the tcp header having known the packet pointer tcp_ptr;

    This is my code :
    SEQ_N=*tcp_ptr <<8 //extract the 1st byte.
    *tcp_ptr ++; // goto next byte.
    SEQ_N=SEQ_N | *tcp_ptr;
    *tcp_ptr++; // 3rd byte.
    SEQ_N=SEQ_N | *tcp_ptr;
    *tcp_ptr++; // 4th byte
    SEQ_N = SEQ_N | *tcp_ptr;
    Well, I am not sure if this would work! Have I done right ? would any one follow the code and tell me if I got the SEQ_N value right ?!1

    Apreciated and kind of help.


  2. #17
    S Sang-drax's Avatar
    Join Date
    May 2002
    Göteborg, Sweden
    Assuming tcp_ptr points to the first byte of the sequence number (first in the TCP package is the port numbers):
    SEQ_N=*tcp_ptr;//extract the 1st byte.
    *tcp_ptr ++; // goto next byte.
    SEQ_N|= *tcp_ptr << 8;
    *tcp_ptr++; // 3rd byte.
    SEQ_N|= *tcp_ptr << 16;
    *tcp_ptr++; // 4th byte
    SEQ_N |= *tcp_ptr << 24;
    Last edited by Sang-drax : Tomorrow at 02:21 AM. Reason: Time travelling

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