Port knocking is an authentication technique to validate a user and open a TCP/IP port to incoming packets. A port knocking sequence consists of a specific number of closed port connection attempts to particular IP addresses. When the correct series of port “knocks” is received, the firewall opens the specific port(s) to the incoming connection request. In addition, port knocking processes commonly also determine if the requesting IP address is on an approved list. One significant benefit of port knocking is that to a hacker scanning a firewall, the service on the port will simply appear not to be available.
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