Good info…here
GNS3 has native support for Linux without the need for need for additional virtualization software
GNS3: Qemu or VirtualBox? … if you keep in mind that was written in 2014. It may still be interesting.
From Wikipedia
QEMU is a free and open-source emulator (Quick EMUlator). It emulates the machine’s processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems.
QEMU copy-on-write (.qcow2, .qed, .qcow, .cow)
QEMU can emulate network cards (of different models) which share the host system’s connectivity by doing network address translation, effectively allowing the guest to use the same network as the host. The virtual network cards can also connect to network cards of other instances of QEMU or to local TAP interfaces. Network connectivity can also be achieved by bridging a TUN/TAP interface used by QEMU with a non-virtual Ethernet interface on the host OS using the host OS’s bridging features.