Problem: You can't add a NAT connection to your GNS3 simulation, and you get the error : "ERROR template_manager:226 Error while creating node from template: NAT interface virbr0 is missing, please install libvirt" Steps to resolve: 1- Create a file named /tmp/default.xml 2- Paste this content and save: <network> <name>default</name> <bridge name="virbr0"/> <forward mode="nat"/> <ip address="192.168.123.1" netmask="255.255.255.0"> <dhcp> <range start="192.168.123.2" end="192.168.123.254"/> </dhcp> </ip> </network> 3- Execute the following commands in your shell : virsh net-define /tmp/default.xml sudo virsh net-start default sudo virsh net-autostart default