Port Knocking!

knock <host> 3000 4000 5000 && ssh -p <port> user@host && knock <host> 5000 4000 3000
Knock on ports to open a port to a service (ssh for example) and knock again to close the port. You have to install knockd. See example config file below. [options] logfile = /var/log/knockd.log [openSSH] sequence = 3000,4000,5000 seq_timeout = 5 command = /sbin/iptables -A INPUT -i eth0 -s %IP% -p tcp --dport 22 -j ACCEPT tcpflags = syn [closeSSH] sequence = 5000,4000,3000 seq_timeout = 5 command = /sbin/iptables -D INPUT -i eth0 -s %IP% -p tcp --dport 22 -j ACCEPT tcpflags = syn

By: din7
2009-07-28 14:08:01

What Others Think

extremely sweet. always. port knocking in da bomb diggity.
linuxrawkstar · 651 weeks and 6 days ago
sameet · 651 weeks and 5 days ago
Nice. Though I prefer ostiary (http://ingles.homeunix.net/software/ost/index.html) for things like that.
namelessjon · 651 weeks and 5 days ago
That's awesome. It adds a security layer against brute forcers.
pyrho · 651 weeks and 5 days ago
That's the correct link to Ostiary btw: http://ingles.homeunix.net/software/ost/ . The one above included the ')'.
pyrho · 651 weeks and 5 days ago
cursed brackets. Thanks for fixing that. :) Ostiary also has a second advantage over port knocking as presented here. You can run it on an unused port (like the telnet port), and use over VPNs, which often block out the high ports often used for knocking.
namelessjon · 651 weeks and 2 days ago
Whoa, what is this voodoo? That is way cooler than I'd imagine.
shurane · 567 weeks and 4 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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