# # (SCO Unix) What is 'port knocking'?
APLawrence.com -  Resources for Unix and Linux Systems, Bloggers and the self-employed

TCP/IP and NFS FAQ

I've removed advertising from most of this site and will eventually clean up the few pages where it remains.

While not terribly expensive to maintain, this does cost me something. If I don't get enough donations to cover that expense, I will be shutting the site down in early 2020.

If you found something useful today, please consider a small donation.



Some material is very old and may be incorrect today

© December 2003 (various)

What is "port knocking"?

Port knocking is a security technique to allow access to people who know the "secret knock". The basic idea is this: packets addressed to certain ports are silently ignored but are logged. If you contact the right series of ports in the right sequence, possibly with the additional condition of holding the ports open for a certain period of time, the firewall rules will be adjusted to allow you access.

The interesting things about this technique include the fact that you can obviously transmit information with the pattern or duration of the "knocks". That means that you could request that some other ip be allowed access, or just request that certain information be sent to you. Another interesting aspect is that because the packets are silently dropped, there's no way to scan a host and determine that it is using a port knocking technique. Even if you knew that it was using such a technique, but didn't know the algorithm, any brute force attempt would be effectively impossible.

A critique of port knocking: http://www.linux.com/articles/37888


If you found something useful today, please consider a small donation.



Got something to add? Send me email.





(OLDER)    <- More Stuff -> (NEWER)    (NEWEST)   

Printer Friendly Version

->
-> (SCO Unix) What is 'port knocking'?


Inexpensive and informative Apple related e-books:

Take control of Apple TV, Second Edition

Take Control of IOS 11

Take Control of the Mac Command Line with Terminal, Second Edition

Digital Sharing Crash Course

Take Control of Preview






Printer Friendly Version

Have you tried Searching this site?

This is a Unix/Linux resource website. It contains technical articles about Unix, Linux and general computing related subjects, opinion, news, help files, how-to's, tutorials and more.

Contact us


Printer Friendly Version





Computers are like Old Testament gods; lots of rules and no mercy. (Joseph Campbell)




Linux posts

Troubleshooting posts


This post tagged:

FAQ

Networking



Unix/Linux Consultants

Skills Tests

Unix/Linux Book Reviews

My Unix/Linux Troubleshooting Book

This site runs on Linode