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QEMU

QEMU is a generic and open source machine emulator and virtualizer.

When used as a machine emulator, QEMU can run OSes and programs made
for one machine (e.g. an ARM board) on a different machine (e.g. your own PC).
By using dynamic translation, it achieves very good performance.

When used as a virtualizer, QEMU achieves near native performances by executing
the guest code directly on the host CPU. QEMU supports virtualization when executing
under the Xen hypervisor or using the KVM kernel module in Linux. When using KVM,
QEMU can virtualize x86, server and embedded PowerPC, and S390 guests.

Networking

VDE2

Open vSwitch

Project site: openvswitch.org

I don't know what-where-how yet. This isn't meant to be a comprehensive how-to anyhow.

Open vSwitch seems to be fairly easy to setup for basic virtual networking, although I can imagine it gets come complicated with OpenFlow and what not. Utilization of tap helps to the easy part. The hard part is rather lack of explanation what-why-how. But I've made it so far, so it can't be that hard

Initialization and start

# just for the first time to initialize DB
ovsdb-tool create /etc/openvswitch/conf.db

# this turns out to be important unless you want to run Open vSwtich in user-space, which I don't want nor know how
modprobe openvswitch

ovs-controller --detach --pidfile punix:/var/run/openvswitch/ovs-controller.sock
ovsdb-server --remote=punix:/var/run/openvswitch/db.sock --pidfile --detach
ovs-vswitchd --detach --pidfile

It's good to omit –detach and run in foreground until you get everything setup and working.

Configuration

I really don't need nor want the basic setup shown all over the intranet. Not for my use anyhow. Oh, btw, br0 gets created auto-magically by ovs-vswitchd.

ovs-vsctl add-br br0

And since I'm not adding eth0, but need to communicate with VMs from the Host and since it doesn't seem like a good idea(?) to give IP address to br0 itself, then:

ovs-vsctl add-port br0 br0-nic -- set interface br0-nic type=internal

In case you need to change port configuration, you don't have to remove it and add it back again. Just do:

ovs-vsctl set port tap0 tag=100
# to verify port settings
ovs-vsctl list port tap0

# display information about switch; similar commands
ovs-ofctl show br0

# ports and their configurations
ovs-vsctl list interface

And that's pretty much it. I find information about switch a bit confusing since it says “current: 10MB-FD COPPER”. Err … right.

As for QEMU ifup/ifdown scripts, they're a bit different than ordinary tap scripts:

# ifup
ovs-vsctl add-port br0 "${1}"
ip link set "${1}" up

# ifdown
ip link set "${1}" down
ovs-vsctl del-port br0 "${1}"

Hooking up with QEMU

Is fairly easy and not different than hooking up tap.

[other QEMU parameters]
-netdev type=tap,id=guest0,script=PATH_TO_UP_SCRIPT,downscript=PATH_TO_UP_SCRIPT 
-device virtio-net-pci,netdev=guest0,mac=RANDOM_VM_MAC

VLANs

Right, the most interesting thing. I only wish somebody haven't decided to use Cisco terminology for VLANs.

Possible values for vlan_mode setting:

access - ``An access port can have only one VLAN configured on the interface; it can carry traffic for only one VLAN.“
trunk - ``A trunk port can carry untagged packets simultaneously with the 802.1Q tagged packets.”
native-tagged - tagged VLAN; equivalent seems to be tag=VLAN_ID (?)
native-untagged - untagged VLAN, resp. tag all traffic VM→port with VLAN_ID (?)

What I haven't figured out yet:

multiple tagged VLANs, default VLAN for untagged traffic
multiple tagged VLANs, no untagged traffic allowed

# untagged VLAN 100; these two commands are equivalent
ovs-ctl add-port br0 tap0 tag=100
ovs-vsctl set port tap0 tag=100
ovs-vsctl set port tap1 tag=100 vlan_mode=native-untagged

# tagged VLAN 100
ovs-vsctl set port tap1 tag=100 vlan_mode=native-tagged

# tagged VLAN 100 and 200
ovs-ctl add-port br0 tap1 trunk=100,200

wiki.zeratul.org

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