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

File-Text Compare and Merge Programs

These kinds of programs can be very useful to the Network Engineer, Technician, Hacker or any Author and Editor.


WinMerge is a free open-source Windows SW one, I used for many years att Siemens and Nokia. And am now adding to my current Laptop and will also look for a version of in on Android for my Tablet.


>>WinMerge is a Windows tool for visual difference display and merging, for both files and directories. It is highly useful for determining what has changed between file versions, and then merging those changes. WinMerge has Unicode support, Flexible syntax coloring editor, Visual SourceSafe integration, and Windows Shell integration. Regexp filtering for filenames and lines. Side-by-side line difference and highlights differences inside lines. A file map shows the overall file differences in a location pane. The user interface is translated into several languages.

Features

• Visual differencing and merging of text files
• Flexible editor with syntax highlighting, line numbers and word-wrap
• Highlights differences inside lines
• Difference pane shows current difference in two vertical panes
• Location pane shows map of files compared
• Moved lines detection
• Compare folders in one level or recursive
• Can show folder compare results flat or in a tree-style view
• <<
  
  Download Link:  https://sourceforge.net/projects/winmerge/
  
  
• Regular Expression based file filters allow excluding and including items
• Compares binary files in folder compare as well as text files
• Shell Integration (supports 64-bit Windows versions)
• Archive file support using 7-Zip
• Fast compare using file sizes and dates
• Creates patch files (Normal-, Context- and Unified formats)