What is port knocking? Port knocking is a method of securing external facing services – explicitly blocked by firewall rules – by enabling firewall access only in the event that a correct sequence of connection attempts to random predetermined ports is attempted. Upon receipt of a correct sequence of connection attempts, the firewall rules are modified on the requested server, temporarily enabling access to the service for the requesting client.
The popular port knocking tool, Knockd, allows users to customize a variety of options to tweak their Knockd deployment. A user might customize the length of the port knocking sequence, the ports specified, the protocol (TCP/UDP), the packet’s flag type(s) (syn, ack, fin…), timeout period, and even an alternate sequence of ports to close the connection.
Before we jump into defining the steps needed to install a Knockd instance, let’s see it in action…
Preliminary Nmap Scan
To start, I have a CentOS machine on my local network (IP – 192.168.1.14) with an SSH server configured and enabled on port 22. Knockd has been enabled and a firewall rule has been configured to block all incoming traffic destined for port 22 (ssh).
Continue reading “Port Knocking & Knockd Configuration”
I wanted to follow up a previous post, where I described the process of configuring a CentOS router for the intention of creating a separate, internal LAN. There we simply deployed a router to separate an external WAN from our LAN and configured the router to pass along all traffic between the two interfaces.
This time I wanted to deploy a router for the purpose of serving content from an internal web server, to an external LAN or WAN.
While this is something that I used recently for a local hackathon, I believe it has greater “real world” application, and can be modified only slightly to accommodate the deployment of other services or applications.
Continue reading “CentOS Router Configuration for a Web Server”
In preparation for an upcoming hackathon, I began working with CentOS as a means to route traffic between two VMware machines: a ParrotOS machine, and a Metasploitable2 machine – both configured on different subnets.
For this tutorial I used the following:
- VMware Workstation 15
- CentOS (Minimal Installation)
CentOS Router Configuration
First, let’s configure the CentOS router to forward traffic between the ParrotOS machine (residing on network 192.168.10.0) and the Metasploitable2 machine (residing on network 192.168.20.0).
Continue reading “CentOS Router: Configuration in Vmware”