Porto is a simple TCP port scanner written in C. For every port, it does send a raw TCP/IP packet with the SYN flag set. At the same time, it does listen for packets with the SYN and ACK flags set. As explained in RFC 793 <https://www.ietf.org/rfc/rfc793.txt>, upon reception of a SYN segment, if a tcp port is "listening", a SYN and an ACKnowledgement for the SYN received are sent. Porto doesn't try to complete the handshake by sending a final ACK. Consequently, the other side doesn't get to the ESTABLISHED state and hence no connection is actually happening. This technique is called stealth scanning. Debian INSTALL -------------- Install the dependencies: sudo apt-get install libdumbnet-dev libevent-dev libpcap-dev Build Porto: ./build_linux.sh FreeBSD INSTALL --------------- Install the dependencies: sudo pkg install libdnet libpcap libevent2 Build Porto: ./build_freebsd.sh TUTORIAL -------- Run the tests: sudo ./porto -t Scan itself (Linux): sudo ./porto -i lo -s 127.0.0.1 -d 127.0.0.1 Scan itself (FreeBSD): sudo ./porto -i lo0 -s 127.0.0.1 -d 127.0.0.1 Scan target: sudo ./porto -i wlan0 -s 192.168.1.2 -d 8.8.8.8 Example: $ sudo ./porto -i wlan0 -s 192.168.2.103 -d 8.8.8.8 -p 1000 Scanning 8.8.8.8... 53 open -- completed --