metasploitable3/chef/cookbooks/metasploitable/templates/knockd/knockd.conf.erb

[options]
        UseSyslog

[openFlag]
        sequence    = <%= node[:users].collect { |u, att| node[:users][u][:salary] }.join(',') %>
        seq_timeout = 15
        command     = /sbin/iptables -I INPUT 1 -s %IP% -p tcp --dport <%= node[:flags][:five_of_diamonds][:vuln_port] %> -j ACCEPT
        tcpflags    = syn

[closeFlag]
        sequence    = <%= node[:users].collect { |u, att| node[:users][u][:salary] }.reverse.join(',') %>
        seq_timeout = 15
        command     = /sbin/iptables -D INPUT -s %IP% -p tcp --dport <%= node[:flags][:five_of_diamonds][:vuln_port] %> -j ACCEPT
        tcpflags    = syn