How to launch multiple QEMU based VM's that can communicate with the outside world and between each other other without any setup on the host.
This uses two features available in qemu
- User Mode Networking stack - SLIRP
- Socket networking backend allows you to create a network of guests that can see each other
This allows us to have
- SLIRP to communicate to the outside world
- multicast to communicate between the VMs
- And it uses the multicast to allow the host to communicate with the guests
VMN=1
qemu-system-x86_64 \
-machine pc,accel=kvm,kernel_irqchip \
-enable-kvm \
-bios OVMF.fd \
-smp sockets=1,cpus=4,cores=2 -cpu host \
-m 1024 \
-vga none -nographic \
-drive file="$IMAGE",if=virtio,aio=threads,format=raw \
-netdev user,id=mynet0,hostfwd=tcp::${VMN}0022-:22,hostfwd=tcp::${VMN}2375-:2375 \
-device virtio-net-pci,netdev=mynet0 \
-netdev socket,id=vlan,mcast=230.0.0.1:1234 \
-device virtio-net-pci,netdev=vlan \
You can add any number of VM's to this socket network, choosing a different value for VMN
You can use socat to create a tap interface on the host with an IP in the same subnet as you want to VLAN to be on and
sudo socat UDP4-DATAGRAM:230.0.0.1:1234,sourceport=1234,reuseaddr,ip-add-membership=230.0.0.1:127.0.0.1 TUN:10.0.3.1/24,tun-type=tap,iff-no-pi,iff-up,tun-name=vmvlan0
This will create a tap interface vmvlan0 on the host with IP: 10.0.3.1
We can run a DHCP server on this tap interface to allow for seamless configuration of the VLAN driven by the host
To assign IP addresss to these VM's from the host you can use dnsmasq serving DHCP on the vmvlan0 interface.
sudo -E dnsmasq --conf-file=dnsmasq.conf --leasefile-ro
strict-order
pid-file=default.pid
except-interface=lo
bind-dynamic
interface=vmvlan0
dhcp-range=10.0.3.100,10.0.3.200
dhcp-no-override
dhcp-authoritative
dhcp-lease-max=253