knockd cheetsheet

Server side

# /etc/knockd.conf
[options]
        UseSyslog

[openSSH]
        sequence    = 3000,4000,5000,6000
        seq_timeout = 15
        command     = /sbin/iptables -I INPUT 1 -s %IP% -p tcp --dport 22 -j ACCEPT
        tcpflags    = syn
        cmd_timeout = 10
        stop_command = /sbin/iptables -D INPUT -s %IP% -p tcp --dport 22 -j ACCEPT


Client side

# Direct network access, knock
knock -v server_ip_address 3000 4000 5000 6000

# Direct network access, nmap
for x in 3000 4000 5000 6000; do nmap -n -Pn --host-timeout 1s --max-retries 0 -p $x server_ip_address; done

# Connect via a squid proxy, nc
for x in 3000 4000 5000 6000; do nc -x 127.0.0.1:3128 -X connect -w 1 server_ip_address $x; done