A small list of free Simulators for Network and Pen Testing.

Image by Pete Linforth from Pixabay 

Network Simulators:

1) Cisco
>>Packet Tracer: Discover and troubleshoot using (The Free Cisco) powerful networking simulation tool.

Enroll, download and start learning valuable tips and best practices for using Cisco’s innovative simulation tool, Packet Tracer. This self-paced course is designed for beginners with no prior networking knowledge. It teaches basic operations of the tool with multiple hands-on activities helping you to visualize a network using everyday examples, including Internet of Things (IoT). Introductory course is extremely helpful for anyone who plans to take one of the Networking Academy courses which utilizes the powerful simulation tool.<<

Ref. https://www.netacad.com/courses/packet-tracer/introduction-packet-tracer



2) GNS3
>> GNS3 is open source, free software that you can download from:  http://gns3.com
GNS3 is used by hundreds of thousands of network engineers worldwide to emulate, configure, test and troubleshoot virtual and real
networks. GNS3 allows you to run a small topology consisting of only a few devices on your laptop, to those that have many devices hosted on multiple servers or even hosted in the cloud<<
Ref. https://docs.gns3.com/1PvtRW5eAb8RJZ11maEYD9_aLY8kkdhgaMB0wPCz8a38/index.html#h.r8cdoew331xy


Pen Testing: Virtual Machines
1) https://www.vulnhub.com/entry/basic-pentesting-1,216/
>>This is a small boot2root VM I created for my university’s cyber security group. It contains multiple remote vulnerabilities and multiple privilege escalation vectors. I did all of my testing for this VM on VirtualBox, so that’s the recommended platform. I have been informed that it also works with VMware, but I haven’t tested this personally.<<

1a) Someone using it, example.
https://alphacybersecurity.tech/basic-pentesting-ctf-walk-through/?fbclid=IwAR0jy7utED6_VN2PK0VwdPdcJhP2S4o680N372zUks_IrPPQLO4oqm4yo78


Virtual Machines:

Portable-VirtualBox: vbox.me
Portable-VirtualBox is a free and open source software tool that lets you run any operating system from a usb stick without separate installation (This is a Windows only tool).

Install Portable VirtualBox to an External Drive.
First, get started by downloading the Portable VirtualBox installer
from vbox.me. Run the downloaded file and extract it to an
external drive or wherever else you want to store your portable
VirtualBox system. You can always move it later if you like.

Ref. https://www.howtogeek.com/188142/use-portable-virtualbox-to-take-virtual-machines-with-you-everywhere/

Other Tools?

I would love to hear about and get download links to other free Simulators that are useful to 
Network learning and or Info-Security, ie Pen-testing or Hacking