[libvirt-users] [libvirt] configuring network interface
Tanguy ROZIER
tanguy at rozier.eu
Thu Feb 10 13:50:25 UTC 2011
Your problem is related to udev : every reboot of VM, udev in VM
checks the MAC address of the ethernet interface of the system to
associate it with a static name (eth0, eth1...).
If you change the MAC address of the Ethernet interface of your VM, it
will detect a new interface and associate it with a new name (ethx+1).
In order to avoid it :
try not to change the MAC address of your VM ethernet device (you can
fix it with libvirt xml),
or deactivate this mecanism in the VM : search in
/etc/udev/rules.d/70-persistent-net.rules : it calls
/lib/udev/write_net_rules at every reboot, you could chmod -x this
script in order to avoid it.
Tanguy
2011/2/10 Marcela Castro León <mcastrol at gmail.com>:
> Hello Laine:
> I've revised the configuration and followed all your instructions.
> I'll try to give you a better explain of my problem.
>
> a) I need a bridged (3) configuration, because I have to connect the guests
> from each others. (via ssh and execute mpi). I've three hosts, each of one
> has at least a guest.
> I'll only explain about the configuration of one of them, because the
> problem is only related a one configuration.
> hostname=rionegro ip=192.168.1.4
> guest-name=rnompi1
>
> b) I've configured host bridge following step by step ther instruction on
> http://wiki.libvirt.org/page/Networking
> this is the /etc/network/config
>
> # The loopback network interface
> auto lo
> iface lo inet loopback
>
>
> auto br0
> iface br0 inet static
> address 192.168.1.4
> netmask 255.255.255.0
> network 192.168.1.0
> broadcast 192.168.1.255
> gateway 192.168.1.10
> bridge_ports eth0
> bridge_stp on
> bridge_fd 0
> bridge_maxwait 0
>
> c) this is the xml guest configuration related to the network.
>
> <interface type='bridge'>
> <source bridge='br0'/>
> </interface>
>
>
> d) But the guest doesn't get any IP automatically, and create an interface
> with a variable name (eth4, eth5,etch6..). I don't know how to achieve the
> guest don't behave like this and create always its network interface with a
> fixed name, for example, eth0).
>
> Why I ask that?
>
> if the guest created an interface with a fixed name, I would configure and
> static ip for the it.
> I'm attaching a printscreen "rnompi1.jpg" that show what ifconfig ahow on
> the guest (eth14 and without any IP). It doesn't get their host either.
>
> The only way I achieve to solve but "temporally" until reboot is configuring
> the guest statically using the name of the interface that has just up.In
> that case every works fine, and the guest can connect to all the other
> guests on the lan and others can connect to it.
> But this only works until reboot or reconfigure the guest, because each time
> the name of interface change, and my configuration I had done of
> /etc/network/interface didn't work any more because is related to another
> interface.
>
> I hope I've explained better the problem I have.
>
> Thank you very much, you've already helped too much to better understand the
> different cases of network configuration
>
> Regards.
>
>
>
>
> 2011/2/10 Marcela Castro León <mcastrol at gmail.com>
>>
>> Hello Laine:
>> Thank you very much.
>> I've showed only one of the guest, each one have it's own ip address.
>> Anyway, I'll follow your advise of revise all the configuration after
>> reading the doc.
>> Thank you very much again.
>> Regards.
>>
>> 2011/2/8 Laine Stump <laine at laine.org>
>>>
>>> (For future questions such as this, you may find you get a better
>>> response (and lower signal-noise ratio) by asking on the recently -created
>>> libvirt-users at redhat.com list, as libvir-list has a very large volume of
>>> patches and discussion about the internals of libvirt)
>>>
>>> On 02/08/2011 12:05 PM, Marcela Castro León wrote:
>>>
>>> Hello
>>>>
>>> I've a lan of virtual machine configured with bridge. I've a private lan
>>> of 4 machine, but one of them have 2 lan-card with access to internet.
>>>
>>> Evertything works almost fine, except that I've configured on each guest
>>> the static configuration of the bridge with the ip address, like this:
>>>
>>> auto lo
>>> iface lo inet loopback
>>>
>>> auto eth6
>>> iface eth6 inet static
>>> address 192.168.1.41
>>> network 192.168.1.0
>>> netmask 255.255.255.0
>>> gateway 192.168.1.10
>>>
>>>
>>> So are you saying that you're attempting to give each guest the *same* IP
>>> address? There's no way that can possibly work, even if each is connected to
>>> a separate virtual network or bridge. Since the host's IP stack can "see"
>>> all of the guests' network traffic, regardless of the connection mode you
>>> choose, each must have a unique IP address even if they can't see each
>>> other.
>>>
>>>
>>>
>>> But each time I, for example, define the guest, it start with a ascending
>>> number of interface: eth6,eth7, eth8, etc, Now is initializing with eth12.
>>>
>>> There must be a mixup in the explanation - I'm understanding that you put
>>> the same config file in each guest, but each guest, when it starts, shows a
>>> different ethernet interface in its ifconfig. That doesn't seem right,
>>> because none of the guests know about each other. Or are you saying
>>> something different? Where are you seeing the "eth6", "eth7", ... "eth12"?
>>> In the guest XML config maybe?
>>>
>>> So, it doesn't get the manual configuration I've done on the
>>> /etc/network/interfaces.
>>> How can avoid this way of work of the number of ethernet interface the
>>> guest start?
>>>
>>> Why are you doing a manual/static definition on the guest at all? It's
>>> simpler to just leave the guest to automatically configure its eth0, and if
>>> you really want a particular IP address for a particular guest, handle that
>>> with a <host> element in the <dhcp> section of the virtual network the guest
>>> is connected to (or, if you're using a pure bridging setup, then in the
>>> static hosts config of the dhcp server on that network).
>>>
>>>
>>> A way i'm trying to solve is configuring the interface trough the guest
>>> xml definition,
>>>
>>> The guest xml interface configuration cannot be used to setup the IP
>>> address, route, etc config of the guest. It is only used for two things:
>>>
>>> 1) configuring what kind of hardware appears on the guest (but not what
>>> name the guest gives to it!)
>>>
>>> 2) configuring how that hardware is connected to the physical network
>>> (usually either via an existing bridge interface on the host (in order for
>>> the guest to appear as if its directly connected to the physical network),
>>> or via a "virtual network" created by libvirt (which is really just a bridge
>>> that's not directly connected to any physical interface, relying instead on
>>> the host's IP stack to route packets from the guest out to the physical
>>> network.)
>>>
>>> but the operation "define" on virsh accepted without error the xml i've
>>> done, but the dumpxml doesn't show them, so, it doesn't work at all.
>>> I've followed the instruction that said the manual "Application
>>> development guide - a guide to application development with libvirt" on page
>>> 71.
>>>
>>>
>>> That document is targeted towards software developers writing
>>> applications to manage virtual guests using the libvirt API, not for system
>>> administrators who are configuring virtual guests manually (or, more likely,
>>> by using software that uses the libvirt API, eg virsh or virt-manager). It
>>> likely contains more detail and less overview than what you need, which is
>>> probably what led to the confusion. I've included a pointer to a wiki page
>>> below that is more the appropriate level of information (Justin, if the docs
>>> you were working on are somewhere easily accessible, you can point to those
>>> instead.)
>>>
>>>
>>> The whole definition of the VM is attached, but the related to interface
>>> is:
>>> <interface type='bridge'>
>>> <source bridge='br0'/>
>>> <target dev='vnet0'/>
>>> <protocol>
>>> <ip address="192.168.1.41" prefix="24"/>
>>> <route gateway="192.168.1.10"/>
>>> </protocol>
>>> <bridge stp="off" delay="0.01">
>>> <interface type="ethernet" name="eth12">
>>> <protocol>
>>> <ip address="192.168.1.41" prefix="24"/>
>>> <route gateway="192.168.1.10"/>
>>> </protocol>
>>> </interface>
>>> </bridge>
>>> </interface>
>>>
>>>
>>> You are confusing the guest interface config (that is part of the guest's
>>> XML config, and described above), and host physical interface config (that
>>> is not in any way associated with guest config, but instead used to
>>> configure the host's physical network interfaces, bridges, bonds, and vlan
>>> interfaces; and nearly as important, is not supported on Ubuntu anyway).
>>>
>>> Actual guest interface config is *much* simpler than that.
>>>
>>>
>>>
>>> But after define, the dumpxml only show this part:
>>> <interface type='bridge'>
>>> <mac address='52:54:00:3c:92:9a'/>
>>> <source bridge='br0'/>
>>> </interface>
>>>
>>>
>>> That's because everything else you've put in your guest config is not
>>> actually a part of a valid guest interface config, and so is ignored.
>>>
>>>
>>>
>>> I would appreciate any help to solve the question. The problem I've is I
>>> lost the access to the guest every time the libvirt change the name of the
>>> interface eth1,2,3, etc.
>>>
>>> In this case I think it may be useful to start over. You've somehow been
>>> tricked into misunderstanding the way that network configuration in libvirt
>>> works, confusing host interface config with guest interface config, and the
>>> resulting config bears little resemblance to what would actually work.
>>>
>>> ==
>>> The first step is to read this page:
>>>
>>> http://wiki.libvirt.org/page/Networking
>>>
>>> to get a basic overview.
>>>
>>> ==
>>> Second step: you should decide which of the three methods of connecting
>>> to guests to the physical network you want to use:
>>>
>>> 1) NATed
>>> 2) routed
>>> 3) bridged
>>>
>>> The simplest is (1), and that will probably work just fine as long as 1)
>>> you don't need incoming connections to the guests, and 2) you're not
>>> concerned about getting the last fraction of an ounce of performance out of
>>> the network.
>>>
>>> Depending on which of those 3 you decide to use:
>>>
>>> ==
>>> Third step: follow the instructions to either create a bridge interface
>>> on the host connected to a physical network interface (for (3)), or to
>>> create a libvirt virtual network using one of the two modes ((1) or (2) -
>>> actually the stock libvirt config already has a "default" network that is
>>> probably adequate for (1), and unless you understand IP routing very well,
>>> you'll likely want to avoid (2)).
>>>
>>> Once the physical network is setup:
>>>
>>> ==
>>> Fourth step: define your guests. In each guest, you'll have an
>>> <interface> element, but it will be much simpler than what you've previously
>>> tried. For bridged mode, the interface section would look like this:
>>>
>>> <interface type='bridge'>
>>> <source bridge='br0'/>
>>> </interface>
>>>
>>> Depending on the guest, you may want to specify what type of hardware is
>>> presented to the guest (default is rtl, which almost always works, but is
>>> not the best perfrorming), in particular, if the guest supports virtio-net,
>>> you'll want to add this into the <interface> element:
>>>
>>> <model type='virtio'/>
>>>
>>> For NATed or routed mode, the guest's interface definition would look
>>> like this:
>>>
>>> <interface type='network'>
>>> <source network='default'/>
>>> </interface>
>>>
>>> (replace "default" with the name of the network you've defined, if you've
>>> defined your own). In this case also, you can add a <model type='...'/> if
>>> appropriate.
>>>
>>> Note that I don't put anything in the <interface> element about MAC
>>> address, target device, or bus address. Those are all setup automatically by
>>> libvirt the first time you start the guest, and it will make sure that the
>>> guests don't interfere with each other.
>>>
>>> ==
>>> Fifth step: only if you need a particular guest to have a particular
>>> fixed IP address, either 1) edit the network config file on the guest, 2)
>>> add a static host to the libvirt virtual network definition (giving the MAC
>>> address provided to the guest by libvirt during the initial guest startup)
>>> with a <host> element added to the <dhcp> element of the network; details
>>> are here:
>>>
>>> http://www.libvirt.org/formatnetwork.html
>>>
>>> or 3) if you're using the bridged method to connect to the physical
>>> network, again either configure the guest's own config file, or add a static
>>> host definition to the dhcp server running on your physical network.
>>>
>>> If you still have problems don't hesitate to send another mail (although,
>>> as I said at the top, sending to libvirt-users at redhat.com may yield better
>>> results than libvir-list at redhat.com).
>>
>
>
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>
--
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Tanguy ROZIER
tanguy at rozier.eu
+33 6 07 26 46 68
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