Why should you use a network simulator
Mobile network simulator
One of the projects I'm currently working on is a mobile network simulator, or GNS3 case for short. I originally built it for a training course that I want to give to colleagues. Later I might use it for a workshop at the GUUG spring technical discussion. In any case, I want to experiment with it myself.
The choice fell on GNS3 because I had already worked with it, even if only briefly. A mobile solution as a suitcase might seem a bit anachronistic, where everything and everyone nowadays stores their data somewhere on the Internet. In fact, I use a GNS3 installation in the case, which is actually intended for servers on the Internet. But more on that later. My intention with this project is to be able to use the simulator even when I don't have internet access. This attitude is partly due to the poor internet connection here in the countryside.
[[! img Error: Image :: Magick is not installed]] The hardware consists of a PC Engines APU 2C4 with housing and power supply unit, a simple aluminum case and a plywood board with spacers on which the APU is attached and a multiple socket. One to three Ethernet cables round off the hardware, depending on requirements.
Right now I still carry a USB to serial converter and null modem cable in case I need to access the APU's console. This is not necessary to work with the case.
Of course, GNS3 is the central element of the software. It is installed according to the instructions for a remote server, that is, via an install script on an Ubuntu 16.04. So it is clear what operating system I am using on the APU. To install Ubuntu 16.04, I followed the instructions from the HowTo Collection from PC Engines.
The APU 2C4 comes with 3 Ethernet connections, which I use as follows:
enp1s0 (Internet) - I installed the operating system via this interface; it is configured externally via DHCP. Since OpenVPN was installed and configured during the GNS3 installation, I can also control the simulations from this side via OpenVPN.
enp2s0 (management) - This interface is configured to the address 192.168.71.1/24. A DHCP server runs here, which supplies connected devices with IP addresses. The computer with the GNS3 client software is usually connected to this interface.
enp3s0 (devices) - This interface is reserved for extended simulations with external devices.
A few firewall settings are necessary for the whole thing to work:
Masquerading to enp1s0
This interface receives an address via DHCP when it is connected to a network. If devices from the management interface are to access resources of the network connected there, they must use the assigned address and thus NAT.
22 / tcp - To shut down the system and for administration, I log in to the APU via SSH.
1194 / udp - The GNS3-VM is accessed via OpenVPN, so this port must be activated accordingly.
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