SSHD & Portknock

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[options]
UseSyslog

[openSSH]
sequence    = 1,2,3
seq_timeout = 5
command     = /sbin/ipset add sshd -exist %IP%
tcpflags    = syn

-A INPUT -p tcp -m multiport --dports 22 -j f2b-sshd
-A INPUT -s 10.0.0.0/8 -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -m set --match-set sshd src -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j DROP

iptables-persistent ipset-persistent