Sending a reset in TCP/IP Socket connection

Question

I am using python’s socket.py to create a connection to an ftp-server. Now I want to reset the connection (send a RST Flag) and listen to the response of the ftp-server. (FYI using socket.send('','R') does not work as the OS sends FIN flag instead of RST.)

Answer 1

Turn the SO_LINGER socket option on and set the linger time to 0 seconds. This will cause TCP to abort the connection when it is closed, flush the data and send a RST. See section 7.5 and example 15.21 in UNP.

In python:

def client(host, port):     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)     s.connect((host, port))     l_onoff = 1                                                                                                                                                                l_linger = 0                                                                                                                                                               s.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER,                                                                                                                                       struct.pack('ii', l_onoff, l_linger))     # send data here     s.close() 

Answer 2

If you want to implement your own behavior over connections I think you should try using Scapy. It is a really useful library/tool. It lets you play with IP/TCP/UDP/ICMP packages.