GNS3
What it is
GNS3 is free, open-source software for emulating, configuring, testing, and troubleshooting virtual and real networks. Its graphical client works with a virtual machine, and servers can run locally or remotely. Users can combine emulated devices running actual images with simulated devices, including a built-in layer 2 switch. Supported vendor appliances include Cisco, Brocade, Cumulus Linux, and HPE. GNS3 also supports Docker instances, QEMU-based appliances, VMware, VirtualBox, Hyper-V, and connections to real networks. Its Marketplace offers preconfigured appliance templates with recommended settings. GNS3 is used for networking education and certification practice, proof of concepts, demonstrations, and interoperability testing. It runs on Windows, macOS, and Linux; documentation recommends the GNS3 VM for most Windows and macOS setups and complex topologies. Users must supply their own Cisco IOS images. The software has no monthly or yearly license fee and does not limit supported devices by license, though practical scale depends on the host computer's CPU and memory. A GNS3 server has no authentication enabled by default and should be restricted at the network level.
For and against
For
- Combines emulated and simulated devices
- Supports multiple vendor appliances and virtualization options
- Can connect to real networks
- No licensed device-count limit
- Available free as open-source software
Against
- Users must provide their own Cisco IOS images
- Server authentication is disabled by default
- Device scale depends on host CPU and memory
The verdict
GNS3 provides flexible network emulation and simulation without a license fee. Plan for host-resource limits, supply any Cisco IOS images yourself, and restrict server access at the network level.
Who it suits
GNS3 suits people practicing networking, preparing for certifications, demonstrating designs, or testing interoperability. It can also support engineers working with virtual and real networks.
Plans and prices
GNS3
Open source · no monthly or yearly license fees · device count limited by available CPU and memory
Read 29 Sep 2026 · docs.gns3.com
On the record
- Appliance marketplace
- The GNS3 Marketplace provides preconfigured appliance templates that use recommended settings and are tested by GNS3.docs.gns3.com · read 29 Sep 2026
- Architecture
- GNS3 consists of a graphical all-in-one client and a virtual machine, with local or remote server options.docs.gns3.com · read 29 Sep 2026
- Cisco image requirement
- Users must provide their own Cisco IOS images; GNS3 says it cannot provide them.docs.gns3.com · read 29 Sep 2026
- Emulation and simulation
- GNS3 supports both emulated devices running actual images and simulated devices such as its built-in layer 2 switch.docs.gns3.com · read 29 Sep 2026
- Integrations
- GNS3 supports Docker instances, QEMU-based appliances, hypervisors including VMware, VirtualBox and Hyper-V, and connections to real networks.docs.gns3.com · read 29 Sep 2026
- Multi-vendor support
- GNS3 supports devices and appliances from multiple network vendors, including Cisco, Brocade, Cumulus Linux, and HPE.docs.gns3.com · read 29 Sep 2026
- Open source
- GNS3 is open source software that users can download and use for free.docs.gns3.com · read 29 Sep 2026
- Platform requirements
- The documentation lists Windows, macOS, and Linux, and recommends the GNS3 VM for most Windows and macOS setups and complex topologies.docs.gns3.com · read 29 Sep 2026
- Purpose
- GNS3 lets network engineers emulate, configure, test, and troubleshoot virtual and real networks.docs.gns3.com · read 29 Sep 2026
- Scale limit
- GNS3 does not limit the number of supported devices by license; the practical limit is the host computer’s CPU and memory.docs.gns3.com · read 29 Sep 2026
- Security
- GNS3 documentation says a GNS3 server has no authentication enabled by default and should be restricted at the network level.docs.gns3.com · read 29 Sep 2026
- Support
- GNS3 points users to its documentation and community for help, questions, and bug reports.docs.gns3.com · read 29 Sep 2026
- Who it is for
- GNS3 is used for networking education and certification practice, proof of concepts, demonstrations, and interoperability testing.docs.gns3.com · read 29 Sep 2026
