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Vnets: Virtual Networks for Virtual Machines
Mike Wray <mike.wray@hp.com>
0) Introduction
---------------
Vnets provide virtual private LANs for virtual machines.
This is done using bridging and tunneling. A virtual interface
on a vnet can only see other interfaces on the same vnet - it cannot
see the real network, and the real network cannot see it either.
Virtual interfaces on the same vnet can be on the same machine
or on different machines, they can still talk. The hosting machines
can even be on different subnets if you run vnetd to forward,
or have multicast routing enabled.
1) Installing vnet support
--------------------------
Assuming the code has been installed (make install in the parent directory),
configure xend to use 'network-vnet' instead of the default 'network' to
start up networking. This just loads the vnet module when networking starts.
In /etc/xend/xend-config.sxp:
Configure the network script:
(network-script network-vnet)
Restart xend.
2) Creating vnets
-----------------
Xend already implements commands to add/remove vnets and
bridge to them. To add a vnet use
xm call vnet_add <vnet config file>
For example, if vnet97.sxp contains:
(vnet (id 97) (bridge vnet97) (vnetif vnetif97) (security none))
do
xm call vnet_add vnet97.sxp
This will define a vnet with id 97 and no security. The bridge for the
vnet is called vnet97 and the virtual interface for it is vnetif97.
To add an interface on a vm to this vnet simply set its bridge to vnet97
in its configuration.
In Python:
vif="bridge=vnet97"
In sxp:
(dev (vif (mac aa:00:00:01:02:03) (bridge vnet97)))
Once configured, vnets are persistent in the xend database.
To remove a vnet use
xm call vnet_delete <vnet id>
To list vnets use
xm call vnets
To get information on a vnet id use
xm call vnet <vnet id>
3) Troubleshooting
------------------
The vnet module should appear in 'lsmod'.
If a vnet has been configured it should appear in the output of 'xm call vnets'.
Its bridge and interface should appear in 'ifconfig'.
It should also show in 'brctl show', with its attached interfaces.
You can 'see into' a vnet from dom0 if you put an IP address on the bridge.
For example, if you have vnet97 with a vm with ip addr 10.0.0.12 on it,
then
ifconfig vnet97 10.0.0.20 up
should let you ping 10.0.0.12 via the vnet97 bridge.
4) Examples
-----------
Here's the full config for a vm on vnet 97, using ip addr 10.0.0.12:
(vm
(name dom12)
(memory '64')
(cpu '1')
(console '8502')
(image
(linux
(kernel /boot/vmlinuz-2.6.9-xenU)
(ip 10.0.0.12:1.2.3.4::::eth0:off)
(root /dev/hda1)
(args 'rw fastboot 4')
)
)
(device (vbd (uname phy:hda2) (dev hda1) (mode w)))
(device (vif (mac aa:00:00:11:00:12) (bridge vnet97)))
)
If you run another vm on the same vnet:
(vm
(name dom11)
(memory '64')
(cpu '1')
(console '8501')
(image
(linux
(kernel /boot/vmlinuz-2.6.9-xenU)
(ip 10.0.0.11:1.2.3.4::::eth0:off)
(root /dev/hda1)
(args 'rw fastboot 4')
)
)
(device (vbd (uname phy:hda3) (dev hda1) (mode w)))
(device (vif (mac aa:00:00:11:00:11) (bridge vnet97)))
)
the vms should be able to talk over the vnet. Check with ping.
If they are both on the same machine the connection will simply
be the vnet97 bridge, if they are on separate machines their
packets will be tunneled in etherip. They should be able to
see each other, but not the real network.
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