In this video I show you how I simulate a real-world company network in GNS3 (Graphical Network Simulator 3). GNS3 is a powerful open-source tool where I can design and test complex network topologies without buying physical routers, switches, or firewalls. I also explain why I like GNS3 for enterprise-style labs: it’s free, it supports real network OS images (like Cisco IOS, Juniper, MikroTik), and the drag-and-drop interface is perfect for CCNA/CCNP practice and real troubleshooting. I walk step-by-step: first I install GNS3 from gns3.com and mention that using the GNS3 VM helps performance. Then I design a small office topology with two routers, two switches (core and access), a firewall (like Cisco ASA), a couple of servers (DNS/web/mail), and a few employee PCs. After that I connect everything with virtual links and use logical naming (HQ, SW1 core, FW1) so the lab stays clean. Finally, I configure the basics—IP addressing, routing (static or dynamic like OSPF/EIGRP), VLANs, trunk/access ports, STP, NAT and firewall rules, and server/PC IP settings (static or DHCP). I also test and troubleshoot using ping, routing tables, link failure simulation, and Wireshark packet capture. The main takeaway: with GNS3 you get hands-on enterprise network design and troubleshooting practice in a safe virtual environment.