Networking in KVM/QEMU

In my previous blog entry, I mentioned about not being able to simply configured networking for the Guest VMs. I feel that area is still unimplemented properly by the GUI wrappers available for KVM/QEMU.

There is a good utility VDE2, which can work great for all your networking needs for the Guest VMs. But unfortunately none of the GUI wrappers (Qemulator, QtEmu, Qlauncher) are handling it.

The simplicity of vde is amazing. Here’s what all you need to do:

iface tap0eth2 inet static
vde2-switch -
#tunctl_user uml-net
pre-up /sbin/iptables -t nat -A POSTROUTING -s -o eth2 -j MASQUERADE;
pre-down /sbin/iptables -t nat -D POSTROUTING -s -o eth2 -j MASQUERADE;
up echo 1 > /proc/sys/net/ipv4/ip_forward
down echo 0 > /proc/sys/net/ipv4/ip_forward

And this is how you’d execute each VM (be it from a wrapper of from the command-line)

rrs@learner:~/bin$ cat virtual-hurd

vdeq kvm -M pc -hda /media/VMIMAGES/Debian_GNU_Hurd.img -m 128 -usb \
-net nic,vlan=1,macaddr=52:54:00:12:02:00 -net vde,vlan=1,sock=/var/run/vde2/tap0eth2.ctl -fda \
/media/VMIMAGES/hurd-floppy.img -boot a

rrs@learner:~/bin$ cat virtual-kfreeBSD

vdeq kvm -M pc -hda /media/VMIMAGES/Debian_GNU_kFreeBSD -m 256 -usb -net \
nic,vlan=1,macaddr=52:54:00:12:01:00 -net vde,vlan=1,sock=/var/run/vde2/tap0eth2.ctl -boot c

rrs@learner:~/bin$ cat virtual-PCBSD

vdeq kvm -M pc -hda /media/VMIMAGES/PC-BSD.img -m 512 -usb -net \
nic,vlan=1,macaddr=52:54:00:12:03:00 -net vde,vlan=1,sock=/var/run/vde2/tap0eth2.ctl -boot c

Interesting things to notice here are the vde2-switch - option in the network configuration section and macaddr=52:54:00:12:03:00 being used with each instance of KVM/QEMU. The macaddr needs to be unique for all the VMs or otherwise you’ll have network lost in all VMs except the one that gets executed last.

As for the tap0eth2 interface, it is very simple. All you’ll need to do is to NAT tap to the interface (eth2 in my case) which talks to the external network.

That’s it. Enjoy the network access in the Guest VMs.

PS: Network access has worked for me in Guest VMs on Hurd, FreeBSD, PCBSD, Minix. These are the only ones I’ve tried till now.