this post was submitted on 19 Apr 2025
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Port knocking is a cool technique
I have used this with second port for handshake (with no info in heading and 20 second times) and then the final port opens with key exchanged from handshake.
Would you use that on internal LAN connections or only external internet facing connections? I'm not aware (not checked) if any firewalls support it... not sure why?
With knockd you can execute arbitrary commands upon a port knocking sequence. So any application that is configurable via terminal is eligible. Here's a tutorial of knockd+iptables (1). Alternativly there's (2) that achieves the same effect in a different way.
You can use it wherever, as part of security in depth. It's essentially a pre-shared secret.
It'll have it's largest effect on publicly facing interfaces. It does not replace having a proper ssh setup (disabling root, disabling password login, etc).
Thanks for the links, I'll take a look as I've never actually played with port knocking.