Latest articles in ‘Virtualization’

  1. Common issues when using virtual machines

    Published: Tue 26 September 2017 in Cookbook.
    A collection of the most common pitfalls and their solutions.

    Qemu issues

    Send the Ctrl-Alt-Del key sequence to the guest

    The Ctrl-Alt-Del is a special key sequence intercepted by he operating system. Windows use it as a security1 measure to unlock its screen, but in the case of virtualized system an alternative is necessary as the key sequence would be intercepted by the host instead of being sent to the guest.

    • If you are using VNC display, press F8, you should get a menu proposing to send the Ctrl-Alt-Del sequence to the guest.

    • If accessibility tools are available, enable the on-screen keyboard, press Ctrl-Alt on your physical keyboard and click Del on the on-screen keyboard.

    • If accessibility tools are not available, on Windows systems press the Shift key at least five times in a row, you should get a pop-up allowing to enable sticky keys. Now successively press the Ctrl, the Alt …

  2. vmtools guided tour, part 2: manage virtual machines

    Published: Thu 21 September 2017 in Projects.
    Learn hos to fork, merge, and otherwise manipulate and diagnose vmtools virtual machines.

    Still with me? In this second part of the vmtools guided tour (read the first part first!), we will now enter in the core of the subject and learn how to manage virtual machines, and in particular how virtual machines forks and merges work.

    As before, if anything seems unclear or would warrant more explanation, feel free to contact me.

    Use vmcreate to create virtual machines

    Create a virtual machine from an installation ISO image

    vmup is useful to boot a virtual disk image, but it doesn’t save the virtual machine settings and does not provide access to vmtools more advanced features.

    In vmtools, a virtual machine is a standard directory gathering a few files. To create a new virtual machine, the most common way is to provide the path to the ISO image of an installation disk and the name of a new directory to create:

    user@host …

  3. vmtools guided tour, part 1: introduction and basic usage

    Published: Mon 18 September 2017 in Projects.
    Install vmtools and use vmup to boot disk image files.

    This the first of a short series of posts introducing vmtools main features. We will start in a gentle way by focusing on a single but central command: vmup.

    Feel free to contact me if anything seems unclear or would warrant more explanation.

    vmtools installation and uninstallation

    Use the provided script to install vmtools on your system. The default is to install it system-wide:

    sudo sh ./

    To install it as unprivileged user, create a ~/.local directory and use it as installation prefix:

    sh ./ -p ~/.local

    To uninstall vmtools, use the provided script.

    Centralized configuration file

    System-wide settings are stored in the file /etc/vmtools/vmtools.conf, this file is optional and must be manually created.

    This file lets you centrally configure the default settings to apply to all your virtual machines.

    Here is an example file:

    # Use VNC as the default display …

  4. vmtools, a Qemu virtual machines manager, is now available

    Published: Sun 17 September 2017 in Projects.

    vmtools is a Qemu virtual machines manager which strives to be easy, versatile and modular while adhering to the principle of least privileges, to respect users’ freedom and security.

    • Easy: Just vmup anything which can be booted, from a local disk image file to remote URLs including .ova archives and devices files. No complex parameters to set or remember, just boots the damn thing.

      Virtual machine settings are saved in short and clean plain-text files. No XML, no unneeded settings, only the non-default values specific to the virtual machine, easily readable and editable with any text editor.

    • Versatile: Use it how you want, vmtools does as few assumptions as possible. No imposed directory structure, no imposed work-flow.

      Saved virtual machines are standard directories and files which can be moved, copied or renamed at will, but can also be freely forked and merged to match even advanced work-flows.

      vmtools commands offer …

  5. How to add Cisco IOS-based devices in GNS3

    Published: Sat 19 August 2017 in Cookbook.
    An explanation on how physical IOS-based devices work and the available solutions to virtualize them.

    GNS3 historical use-case was to act as a GUI around Dynamips to emulate Cisco devices. However, while stable, this emulation may not be as straightforward as it could be and has some limitations.

    To understand the negatives, we first need to understand how IOS-based Cisco hardware work.

    How real gear works

    Professional switch and router devices cannot be reduced to a general purpose small-factor computer with a few additional network interfaces.

    When using a general purpose computer with classical network adapters to build a router/firewall appliance, all the processing occurs at the software level, generally the operating system kernel.

    On specialized hardware such as Cisco switches and routers, the operating system (here IOS) works tightly with some underlying specific (and usually proprietary) hardware and delegates parts or all of the processing to dedicated chips, the Application Specific Integrated Circuits or ASICs, to allow faster processing.

    On general-purpose computers …

  6. How to add virtual machines (end devices nodes) in GNS3

    Published: Mon 14 August 2017 in Cookbook.
    Updated: Mon 25 September 2017 (Improved "Create your own virtual machine")
    All you need to know to use virtual machines inside GNS3 topologies.

    Virtual machines can be added in GNS3 topologies as end devices nodes and can play various roles:

    • Lightweight ones are very focused for instance to provide just enough to test the network connectivity or provide a functional browser.

      They start blazingly fast and are very light on resources, meaning you can put several of them to test end-user workstation behavior at several places in your topology with little to no worry about the CPU or memory impact.

    • Dedicated appliances are designed to provide a specific service, like networking (firewall, …), applicative (proxy, email filtering, …) or administrative (monitoring, …) services.

      Resource consumption vary greatly depending on the service and the software used by the appliance. However, professional appliances are usually designed to handle a large number of simultaneous operations: some will support with no issue to see the virtual machine resources settings reduced on test environments (some may require a modification in their …

  7. Where to find virtual machines and ISO files?

    Published: Mon 14 August 2017 in Cookbook.
    Updated: Thu 23 November 2017 (Add atrick for older Microsoft download URLs)
    The best places to find ISO images and ready-made virtual machines to feed your virtual lab.

    Free software

    Virtual machines

    Several websites offer a large selection of freely downloadable virtual machines with pre-configured free software, for instance:

    You can also check the marketplaces maintained by virtualization-related software, such as VMware and GNS3.

    ISO files

    Obviously the main place to get free software ISO files is from the projects website.

    However, FrozenCow maintains a centralized list of direct links to a fair number of Linux and BSD installation ISO files.

    Some projects host all previous versions of their system, but sometimes they are not easy to find. Search in priority on the master repository as these older versions may not be copied onto mirrors. Sometimes they are stored in a separate “archive” area. At last, WinWorld does a great job in collecting old systems installation medias, including discontinued Linux distributions.

    If you are not sure which Linux or BSD system to choose, DistroWatch might …

  8. How to install GNS3 and VMware Player on Linux (Debian)

    Published: Sat 12 August 2017 in Cookbook.
    Updated: Sat 19 August 2017
    Step-by-step guides to install GNS3 and/or VMware player on Linux.

    While installing GNS3 and VMware should be easy, it in fact very easy to loose a lot of time on silly issues.

    • If you are interested only in installing VMware Player, feel free to directly go corresponding part.

    • If you are interested in installing GNS3, I also recommend to install VMware player as some appliances may require it.

    RouterGods also shared a few tips on how to setup a more comfortable GNS3 lab. Take a few minutes to check it once you’ve ended the installation!

    Installing GNS3

    GNS3 relies on Linux kernel features. If you are not a Linux user, the recommended way to use GNS3 is to use the GNS3 official virtual machine. This virtual machine may also be a good solution if you are a Linux user but you just want to quickly test GNS3 or do not want to modify your host environment.

    For a regular …

  9. How to build a virtual pentest lab

    Published: Fri 11 August 2017 in Cookbook.
    Updated: Sat 19 August 2017
    A guide to choose the best hardware and software to match your needs at the lowest cost and efforts.

    Standalone virtual machines are both a cheaper and more practical solution to test systems as they doesn’t need to dedicate hardware and are easier to handle than physical installation (actions such as cloning, doing a snapshot or a rollback become trivial).

    Network virtualization goes a step further and apply the same system to a whole network, including workstations, servers, and all networking devices such as switches, routers and firewalls. A virtual network can be of any size and topology, and can mimic any real-life situation such as Active Directory domains, remote-access or site-to-site VPNs or test protocols of every network plane.

    Such virtual network can be either fully isolated or have one or several link to physical devices and networks, its all up to you to decide.



    The goal of a virtual lab is to be able to quickly setup the environment which will allow you to …

  10. How to run a CAM table overflow attack in GNS3

    Published: Sun 26 June 2016 in Cookbook.
    Updated: Sat 19 August 2017
    Background information on CAM table overflow attacks and concrete steps to reproduce them in a GNS3 lab.

    Knowing where difference with real gears lies

    For performance reasons, a lot of switch things are actually not part of the IOS code but are implemented in hardware. This includes the ARL, or Address Resolution Logic, which provides all the methods to add, remove and lookup entries in the MAC address table.

    Therefore, for the NM-16ESW module to work in GNS3, Dynamips had to reimplement all these normally hardware provided services, or at least push this far enough to allow an unmodified IOS to run on it correctly.

    The sad thing is indeed that this is unfinished work, as stated in this module’s source code header:

     * Cisco router simulation platform.
     * Copyright (c) 2006 Christophe Fillot (
     * NM-16ESW ethernet switch module (experimental!)
     * It's an attempt of proof of concept, so not optimized at all at this …

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