Lower than low level common bsd sockets

Question

How do you do low low level sockets in C, example: actually sending a SYN.

Answer 1

What you actually want is a raw socket ... you can completely control the headers and flags with the raw socket interface, but programming them is much more challenging. Here's a great tutorial to get you started: http://www.cs.binghamton.edu/~steflik/cs455/rawip.txt.

Answer 2

Raw sockets are your friend.

There have been some links to useful information on this question.

Also consult Chapter 25 "Raw sockets" of Steven's "Unix Network Programming"

If you're attempting cross platform code you may find libpcap a useful alternative.