#!/usr/bin/python

import scapy.all as scapy
import random
import time
import subprocess


def send_response(t):
    t.src, t.dst = t.dst, t.src  # swap ethernet addresses
    ip = t.getlayer("IP")
    ip.src, ip.dst = ip.dst, ip.src
    t.dport, t.sport = t.sport, t.dport
    t.getlayer("TCP").flags |= 0x10  # set the ACK flag
    t.ack = t.seq + 1
    del t.getlayer("TCP").chksum
    scapy.sendp(t, iface="eth0", verbose=False)

print("Filtering input from 10.0.0.1...")
subprocess.call("iptables -I INPUT -s 10.0.0.1 -j DROP", shell=True)

try:
        scapy.sniff(filter="host 10.0.0.2 and tcp[tcpflags] == tcp-syn",
                    iface="eth0", prn=send_response, store=False)
finally:
        print("Accepting input from 10.0.0.1 again...")
        subprocess.call("iptables -D INPUT -s 10.0.0.1 -j DROP", shell=True)