I use netfilterqueue in my code. I downloaded the libraries by using pip install NetfilterQueue and implemented them in my code by typing from netfilterqueue import NetfilterQueue And I run the code, it gives me this: $ sudo python3 waff.py [sudo] password for misbahskuy: Traceback (most recent call last): File "/home/misbahskuy/waf-coba/waff/waff.py", line 1, in <module> from netfilterqueue import NetfilterQueue ModuleNotFoundError: No module named 'netfilterqueue' I used a method to solve it by uninstalling the code and installing it again. I also restarted my Kali, and it's the same; it doesn't provide success. And this is my code: from netfilterqueue import NetfilterQueue from dpkt import ip q = None nfqueue = NetfilterQueue def cb(dummy, payload): # make decision about if the packet should be allowed. in this case, drop everything: payload.set_verdict(nfqueue.NF_DROP) q = nfqueue.queue() q.open() q.bind() q.set_callback(cb) q.create_queue(1) q.try_run() Continue reading...