in reply to Re^2: Piggybacking data on TCP ACK
in thread Piggybacking data on TCP ACK

I think we are using the same terminology to refer to 2 different things. After a connection is made:

A B SYN------> <--------SYN+ACK ACK------>

Then the ACK flag (or bit) is kept high for all subsequent packets. I used the term ACK to mean specifically the packet sent in response to a SYN+ACK packet, I did not mean to use it to refer to any packet with the ACK flag set.

You are correct that data is allowed to be sent during the 3 way handshaking provided that it remains in a buffer until the connection is established (from RFC 793). So the data does (should) not be passed up the stack until the connection is made.

I currently do not have access to a computer with the libpcap library but this code should help get you started towards your goal.

use Net::RawIP; $ack_with_data = Net::RawIP->new({ ip => { saddr => '', daddr => '' }, }); tcp => { source => 111, dest => 111, ack => 1, #insert the correct seq number and ack seq number seq => 11111, ack_seq => 11111, #insert http data here (i am not very familiar with http) data => "GET /asdlfk HTTP/1.1\nHost:\n", }, }); $ack_with_data->send;

Disclaimer: This code might be missing some things. I was not able to test it but it should help you see how to form a packet and send it. The specific fields will need to be correctly set and I might be missing a few.