It's just caution. Using port knocking by itself would be a recipe for security disaster. As an addition to an already secure system, it's okay if you just want to reduce junk in your logs, perhaps. Many would ask, in that case, why use port knocking at all?
The is the usual thing I hear. It is so incredible naive, though.
Any service, no matter how locked down and properly configured, still presents an attack surface. SSHD is a program like any other, and it can have bugs.
When you use port knocking with a properly configured SSHD, you are much more secure because that attack surface has been removed.
Port knocking has been mentioned before on HN and it generally gets a luke warm to negative response. It completely baffles me, this response.
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