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Knock: TCP Port Knocking Proposed For Linux Kernel

Linux Kernel

Published on 10 December 2013 01:55 PM EST
Written by Michael Larabel in Linux Kernel
4 Comments

A "Knock" patch has been proposed for the mainline Linux kernel that would provide NAT-compatible, TCP stealthy port knocking for improved network security of Linux systems.

Port Knocking is the process of opening network ports on a firewall by first attempting to connect to a set of predefined unopen ports. It's effectively a key for opening network ports with the password being the pegging of other closed network ports in the correct sequence.

There's know a "Knock" patch for the Linux kernel that would unify this capability within the Linux kernel. Generally, port knocking is handled by a user-space daemon monitoring firewall logs for failed connection attempts. Knock is designed to be stealthy, done completely within the Linux kernel and only activated by a single extra setsockopt call, can be used for protecting the first N-bytes of the TCP payload, is designed to work behind NATs, and is a free, simple kernel modification. The disadvantage to the Knock design is self-admitted that the TCP SYN packet's SQN is only 32-bits long and would be subject to brute force attempts but involving billions of network packets.

Plenty more details on the proposed Knock port knocking for the Linux kernel can be found via the kernel patch submission and the Knock project page.

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
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