# Port knocking To enable a port, an adversary sends a series of packets with certain characteristics before the port will be opened. Usually this series of packets consists of attempted connections to a predefined sequence of closed ports, but can involve unusual flags, specific strings or other unique characteristics. After the sequence is completed, opening a port is often accomplished by the host based firewall, but could also be implemented by custom software. **Example:** `for x in 7000 8000 9000; do nmap -Pn --host_timeout 201 --max-retries 0 -p $x 10.10.10.10; done` OR `ports="40809 50212 46969"; for port in $ports; do echo "a" | nc -u -w 1 10.10.10.96 ${port}; sleep 0.5; done; echo "knock done"; nc -w 1 -nvv 10.10.10.96 22` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://infra.newerasec.com/infrastructure-testing/gaining-access/port-knocking.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.