Quote Originally Posted by prof.ebral View Post
I also like having the option of being able to code my own firewall.
But do it with means meant for coding a firewall, not a userspace application.

The OP can thread the connections and when a connetion attempt is made to a port he can be notified, release the port, and allow the connection to proceed.
Hmm? Could you share a snippet of that does what you mean? Where would the connection proceed exactly? It seems you are using unix, so let's assume netcat started as
bash Code: 
  1. netcat -l 10001
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... to be our server. Please write a minimal application (using whatever technology available for a standard u*ix system) that will bind a userspace application to tcp port 10001, intercept the connection, issue some debugging statement to the console and let the connection be picked up by the netcat pseudo-server.

Please also perform a (shallow) theoretical analysis of how the tcp handshake (SYN ->, SYN+ACK <-, ACK ->)would look like from the client's perspective in such a situation.