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GNS3

Free, open-source network emulator for building virtual labs of real router and switch images.

Open sourceSelf-hostableNetwork simulators and emulators
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About GNS3

GNS3 is a free graphical network emulator used by network engineers and certification students to build virtual topologies of routers, switches, firewalls and hosts on their own computer. Rather than simulating device behaviour, it runs real network operating system images (Cisco IOS through Dynamips, plus QEMU, VirtualBox, VMware and Docker nodes), so labs behave much like the hardware they copy. You draw a topology in the desktop client and run it on a local server or in the GNS3 VM, which is needed for heavier images and bigger labs; a single server can also be shared by several clients. The project is open source under GPL v3, with clients for Windows, macOS and Linux and an appliance library of ready-made device templates. GNS3 itself costs nothing, but you have to supply licensed vendor images, which is the main hurdle compared with Cisco Packet Tracer. Large labs need a lot of RAM and CPU, and the Mac build is unsigned, so first launch takes extra steps.

Best for: Network engineers and CCNA/CCNP students who want free labs running real device images.

Pros and cons

What works

  • Free and open source under GPL v3
  • Runs real vendor images, not a simplified simulation
  • Mixes Dynamips, QEMU, VirtualBox, VMware and Docker nodes
  • One server can be shared by several clients

Why people leave

  • You must source your own licensed router and switch images
  • Bigger labs need a separate VM and lots of RAM
  • Mac version is unsigned and needs Gatekeeper workarounds

Top GNS3 alternatives

See all 2
  1. 1EVE-NG logo
    EVE-NG

    Browser-based, clientless labs on a dedicated server, with multi-user features in the paid edition.

    66.5
  2. 2Ci
    Cisco Modeling Labs

    Cisco's own simulator ships licensed Cisco images, so you don't have to hunt for them yourself.

    62.6

Why people left GNS3

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GNS3: common questions

Is GNS3 free?

Yes. GNS3 is free, open-source software that you can host yourself.

Is GNS3 open source?

Yes. The source code is on GitHub at GNS3/gns3-gui. You can also run it on your own server.

What platforms does GNS3 run on?

GNS3 is available for Windows, macOS, Linux and Self-hosted.

What are the best alternatives to GNS3?

The highest-ranked GNS3 alternatives right now are EVE-NG and Cisco Modeling Labs. See the full ranked list for pricing, platforms and verified facts.

See all 2 GNS3 alternatives