Based on this question: "Safe mode" on Linux? - So there is a configured knockd on a server, and a wrong firewall command was given out, so everybody got locked out from the server via layer3 (iptables). OK.
Could this be resolved by knocking the ports as in the knockd, so then the knockd will open given ports? Could this be a last chance to get in to the server via layer3?
Or it will not work, because if ex.: knockd configured to use port 5000 and port 5000 is blocked on all protocols, knockd will not work? Is knockd "before" the netfilter? (I mean INTERNET->KNOCKD->NETFILTER?)