First, confirm that the default network is indeed inactive:

sudo virsh net-list --all

If yes, just start the default network:

sudo virsh net-start default 

Run the first command again to see if it worked.

If the default network is not autostarted, just enable this:

sudo virsh net-autostart default


[1] Can’t start KVM guest: “network ‘default’ is not active”

[2] How to fix “network ‘default’ is not active” error in libvirt