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Old 12-09-2015, 01:47 AM   #1
wh33t
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Question Close and open ssh port remotely - most likely advanced


Hey LQ,

Back in the day I used to work for a small tech company that made hardware firewalls. The only way to communicate with the firewalls themselves was to ssh into them. The techs had the SSH port closed until what they called a "knock packet" was received by firewall. When the knock packet was received it would open up an ssh listening port for 30 seconds. If the connection wasn't made within 30 seconds the port would close again.

I was just a lowly tech grunt that built servers and networked office printers at the time and unfortunately never learned the tech behind it. But I'm really interested in setting something like that up now.

What is involved in setting something like this up?
 
Old 12-09-2015, 02:02 AM   #2
berndbausch
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It's called port knocking. A lot of cookbooks are available, for example https://wiki.archlinux.org/index.php/Port_Knocking. If that link is not satisfactory, search for "linux port knocking".
 
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