Qemu is a generic and open source machine emulator and virtualizer. It is used by GNS3 to run Cisco ASA, PIX and IDS as well as any conventional operating system. Note that Qemu must supports UDP tunnel networking in order to be used from within GNS3 and the good news is that it is already supported since Qemu version 1.1, the bad news is that recent versions do not work very well to emulate ASA and IDS on Windows and Mac OS X.

Qemu binaries

Qemu releases before version 1.1 must be patched to work with GNS3. For your convenience, we provide patched versions of Qemu:

Windows (32-bit)

The most stable and recommended version is 0.11.0 which is already included in the GNS3 all-in-one.


Recent Qemu versions >= 1.1 should work very well on Linux, especially with the KVM module enabled. Alternatively, you can use this following version.

Mac OS X

These are the most stable and recommended versions of Qemu for OSX, they are already included in the GNS3 DMG.


Here are some available patches for the brave who want to compile and patch Qemu themselves.


Pemu or PIX emulator is a old modified version of Qemu (0.9.0) that can run Cisco PIX firewall images. In GNS3, Pemu is totally independent of Qemu and included by default in our Windows all-in-one. Note that Pemu is not available for Mac OS X and must be installed on Linux platforms.