Cisco Packet Tracer vs GNS3: which to use for CCNA

Cisco Packet Tracer and GNS3 both let you build networks on a PC, but they work in different ways. Packet Tracer simulates Cisco devices inside one program. GNS3 emulates them by running real network operating systems. This page explains what that means for your study, with Packet Tracer facts taken from Cisco's own pages as of October 2026.

The short verdict

• Start with Packet Tracer if you are new to networking or following a Cisco Networking Academy course. It is free, legal, light, and its simulation mode shows you every packet.
• Move to GNS3 (or Cisco Modeling Labs) when you need real IOS behaviour, non-Cisco devices, Linux hosts or larger labs, and you have licensed images.

Most CCNA candidates use both at different stages.

At a glance

Simulation vs emulation

This is the core difference. Packet Tracer's help files describe it as "a medium fidelity, network-capable, simulation-based learning environment" for "a CCNA-level of complexity". They also say plainly that it "relies on a simplified model of networking devices and protocols" and that real networks remain the benchmark.

So the routers in Packet Tracer are not running IOS. They run Cisco's model of IOS, with a large but limited set of commands. In the same help page, Cisco marks several protocols as having "substantial modeling limitations", including STP, RSTP, TCP, IPv4, IPv6, PPP and multilayer switching.

GNS3 runs the real software. An IOSv router in GNS3 is IOS in a virtual machine, so every command, bug and timer behaves as on that version. The cost is that you need the images and enough CPU and RAM to run them. If you want the theory behind this split, see network emulation vs simulation.

Getting each one

Packet Tracer

Cisco distributes Packet Tracer through Cisco Networking Academy. The free, self-paced course "Getting Started with Cisco Packet Tracer" says to enrol to download it. The NetAcad Resource Hub then lists Packet Tracer 9.0.1 for Windows, macOS and Ubuntu (64-bit), behind a login. When you first launch it, you click the Skills for All button to sign in.

Cisco's listed system requirements are Windows 11, macOS 12 or newer, or Ubuntu 22.04 or 24.04 LTS, an amd64 (x86-64) CPU, 4 GB of free RAM and 1.4 GB of free disk space.

GNS3

GNS3 is a free download for Windows, macOS and Linux, released on GitHub under GPL-3.0. On Windows and macOS, IOSv, IOU and most appliances run inside the GNS3 VM, which GNS3 recommends running in VMware so it can use nested virtualization. Then you add images. GNS3 ships none, and you must use images you are licensed to run in GNS3. Cisco's CML-Free documentation states that the images that come with Cisco Modeling Labs are only licensed for use within CML.

Setup is the hard part of GNS3. Our GNS3 troubleshooting guide covers VT-x, KVM and VM version errors.

What Packet Tracer does well

• Seeing packets move. Simulation mode stops time. You add a PDU, step through events, and open each packet by OSI layer. For learning ARP, DHCP, STP or ACL behaviour, nothing is clearer.
• CCNA coverage. The protocol list includes VLANs, 802.1Q trunking, VTP, DTP, EtherChannel, RIP, EIGRP, single and multi-area OSPF, BGP, NAT, ACLs, DHCP, SSH, IPsec and QoS features.
• Wireless, IoT and the physical view. You can place devices in buildings and wiring closets, and version 9.0 added industrial devices and protocols plus a Cisco C8200 router model.
• Graded activities. The Activity Wizard builds self-scoring labs, which is why NetAcad courses use it.
• Light hardware. Cisco's stated minimum is 4 GB of free RAM and 1.4 GB of disk.

What Packet Tracer can't do

• Run real images. You cannot load IOS, IOS XE, NX-OS or another vendor's OS.
• Run full Linux or Windows hosts. PCs have a Command Prompt utility and servers offer menu-configured services (DHCP, DNS, HTTP, TFTP and others), but they are models, not real operating systems.
• Match every command and behaviour. Expect some commands and behaviours to differ from real IOS. The help files flag the protocols with substantial modeling limitations.
• Give you a real capture. You inspect packets in simulation mode's event list and PDU views, not in a capture you open in Wireshark.
• Share topologies with other tools. Labs are saved in Packet Tracer's own .pkt format.

What GNS3 does well, and its limits

GNS3 runs Dynamips, IOU, QEMU/KVM, VirtualBox, VMware and Docker nodes, so you can mix Cisco routers with Linux servers, firewalls and other vendors. You capture with Wireshark on any link, and packet filters add delay, jitter, loss or corruption.

Its limits are the flip side. You need licensed images, and IOSv-class images need hardware virtualization. On an Apple Silicon Mac, x86 images do not run at a usable speed; see GNS3 on Apple Silicon. And GNS3 has no simulation mode: you learn from captures and debug output instead of animated packets.

Which to pick

• First networking course or early CCNA study: Packet Tracer. It is free, legal and built for it.
• Labs your course hands you as .pkt files: Packet Tracer, since the activities and grading live there.
• Troubleshooting practice that should feel like real routers: GNS3 with images you are licensed to use, or CML-Free if you need Cisco images legally.
• Mixing Cisco with Linux servers or other vendors: GNS3.
• An old or low-RAM laptop: Packet Tracer.

Our guide to CCNA labs without Cisco hardware goes through every legal option, including CML-Free.

Where Isothrum fits

Isothrum's editor is a free browser editor for emulated labs, not a simulator. You draw containers, Linux and Windows VMs, switches with VLANs and trunks, and FRR or Cisco routers from your own images, then export Docker Compose, Vagrant, Proxmox, Kubernetes or cloud files to run them. It opens GNS3 projects but not Packet Tracer files. It suits the step after Packet Tracer, when you want real software and plain files you can rerun.