apt-get install knockd


apt-get install tcpd


ldd /usr/local/filename | grep libwrap


#  UseSyslog
logfile = /var/log/knockd.log


/usr/bin/perl -ni -e 'print unless /SSHD: %IP%/' /etc/hosts.allow


/usr/bin/perl -ni.bak -e 'print unless /SSHD: %IP%/' /etc/hosts.allow


KNOCKD_OPTS="-i eth0"


START_KNOCKD=1


OPTIONS=" -d -D"


service knockd restart


watch -n1 cat /etc/hosts.allow


knock -v 12.34.56.78 1022 3022 3024


knock -vu 203.1.2.3 2022 3022 3022


knock myserver.example.com 123:tcp 456:udp 789:tcp


one_time_sequences = /etc/knockd/one_time_sequences


cmd_timeout = 10