A year back, I started preparing for my Cisco Certifications, that is when I got to know about this beautiful tool called, GNS3.
In my setup, I have got GNS3 v2.1.6 installed on my laptop, and have GNS3 VM installed for VMware Workstation. You can google for IOS/U images. I do not have the link handy but I remember somebody had shared Google Drive link for images, I downloaded from there.
For GNS3 to work flawless, minimum RAM of the Laptop should be 8GB.

Purpose of this article: Sometime back, I came across the error wherein GNS3 wasn’t loading & was throwing an error stating “The NPF or NPCAP service is not installed, please install Winpcap or Npcap and reboot.”
That time, I did some research on Google & had to uninstall & install some components & had to reboot my laptop, which fixed the issue.
Recently, after a silent Windows update, I got the same error again.

gns3 error
Resolution:
Found out that, there is a service within the Windows Box which need to be restarted to fix the issue. All you need to do is close GNS3 tool & run below 2 commands from a “command prompt” window launched as admin.

net stop npf
net start npf