TCP Syn in Raw Socket 1

[fman23]

I tried to send a TCP Syn packet to a port to initiate a handshake.
But I never got the reply from the target port.. (I was using WinDump to monitor net traffic)
I thought perhaps the Syn packet was not properly constructed, so i tried to imitate the Syn packet sent by NMapWin.. (the hex dump is like below):

45 00 00 28 46 2D 00 00 27 06 20 EB 0A 7E 0B E9 0A 7E 0B D4 86 2A 00 01 35 B3 29 68 00 00 00 00 50 02 10 00 8D E3 00 00

But there's another problem.. the checksum field (octet[11..12] = "20 EB" and octet[37..38] = "8D E3") is not the same.. (mine was "6B 06" and "00 00" respectively).
So i assume the packet was dropped by target host because CRC error..

Is my assumption correct?

Can anyone help me how to construct the proper TCP packet (header)? especially the checksum method..

thx in advance..

 

[bcastner]

http://www.netfor2.com/tcp.htm

 

[fman23]

Thx... it was a great help..

my packet finally acknowledged...

and i also found a tutorial by San Bergmans that describes TCP/IP theory in a very easy way to understand (IMHO)..

http://www.xs4all.nl/~sbp/projects/tcpip/theory/theory1.htm

although some part of it are still under construction.

 

[bcastner]

Thank you for the link in return.

Best,
Bill