The sys admin's daily grind: Knockd

Knock-Knock

Article from Issue 94/2008
Author(s):

Horror stories are full of scary characters knocking on doors at night. On Linux, we just call this port knocking, and it can actually be quite useful.

If you prefer not to have an obvious administrative port for your iptables firewall – but do need a secret one – port knocking is an interesting option that can put off script-based attacks. For the ambitious but secretive admin, the tool of choice is Knockd [1].

The package includes two components: Knock is the client that sends knocking signals, which the Knockd daemon receives.

Knocking

To monitor the process, Knock, the knocking client, only needs the port number on which to knock and a -v option.

[...]

Use Express-Checkout link below to read the full article (PDF).

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

SINGLE ISSUES
 
SUBSCRIPTIONS
 
TABLET & SMARTPHONE APPS
Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Charly's Column

    Conventional, woodpecker-style port knocking is open to sniffing and brute force knocking attacks. Sending an encrypted packet with an access request to the server is safer and more modern. Learn more about Firewall Knock Operator, a.k.a. Fwknop.

  • Single-Packet Port Knocking

    If you are looking for an extra layer of remote access security, try single-packet port knocking.

  • Charly’s Column: PortSentry

    To celebrate 10 years of his column, Charly sets up a sensitive detector that measures the cosmic background radiation of the Internet.

  • The sys admin's daily grind: DenyHosts

    When it comes to warding off unwanted login tests on SSH port 22 and others, Charly likes to keep an ace or two up his sleeve by relying on DenyHosts instead of Fail2ban.

  • Charly's Column – Whowatch

    For no particular reason, Charly occasionally patrols his server farm and hunts down attackers. He has put together a neat toolbox for this job.

comments powered by Disqus
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters

Support Our Work

Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

Learn More

News