[libvirt] The config of IP address for 'macvtap' network

[Lei Li]

On 05/15/2012 11:12 PM, Laine Stump wrote:
> On 05/15/2012 05:33 AM, Michal Privoznik wrote:
>> On 15.05.2012 10:57, Lei Li wrote:
>>> Hi guys,
>>>
>>> I know the macvtap network is supported by libvirt as forward mode
>>> 'passthrough', I wonder is there anyway to configure the IP address
>>> for its interface?
>>>
>>> For example, If I create a network as below:
>>>
>>> <network>
>>>    <name>vdsm-testnet</name>
>>>    <uuid>31f6b3b3-e959-0dd1-ad3a-bf95db660415</uuid>
>>>    <forward dev='eth0.8' mode='passthrough'>
>>>      <interface dev='eth0.8'/>
>>>    </forward>
>>> </network>
>>>
>>> For now, I have to set the IP address by 'ifconfig eth0.8 XXX.XXX.XXX.XXX'
>>> after defining the network.
>
> If only the guest will use the interface, that isn't necessary. As a
> matter of fact, once an interface has been assigned to a guest using
> macvtap passthrough mode, the host *can't* use the interface (it can
> continue to use it in the other macvtap modes, however), so it's
> completely pointless to configure an IP address for that interface on
> the host.
>
>
>>> How can I set IP address for this VLAN device 'eth0.8' by libvirt, I mean
>>> does libvirt support to assign IP address in this mode now? If does,
>>> what is the
>>> xml format for it?
> A network device being used for a guest macvtap connection only needs an
> IP address set on the host if the host will also be using that interface
> - the guest does not magically acquire/use the IP address that has been
> set on the host, it needs its own IP address, configured on the guest in
> the same fashion you would configure any other guest interface (keep in
> mind that even in macvtap 'bridge' mode, the host and guest cannot
> communicate with each other via a macvtap interface). Otherwise, it's
> enough for the interface to be defined on the host (it may also be
> necessary for it to be "up" if it's a vlan device - I haven't tried
> macvtap with vlans). If you are using RHEL or Fedora, you can do any/all
> of that configuration with the virsh iface-define command. For example,
> here is the xml file that would define an "eth0.8" interface on a host
> (This is *not* the<interface>  element of a domain configuration):
>
>
> <interface type="vlan" name="eth0.8">
>    <start mode="none"/>
>    <protocol family="ipv4">
>      <ip address="192.168.43.1"/>
>    </protocol>
>    <vlan tag="8">
>      <interface name="eth0"/>
>    </vlan>
> </interface>
>
> To get this defined in the system, you would use:
>
>     virsh iface-define eth0.8.xml
>
> But again, it seems doubtful this is what you really want.
>
>>> It'd appreciate a lot if anybody could read my post and give me some
>>> suggestions!
>>>
>>>
>> I suppose adding:
>>
>>   <ip address='192.168.123.1' netmask='255.255.255.0'/>
>>
>> into<network/>  should work, doesn't it?
> No.
>
> The IP address used by the host for that interface (if any) should be
> configured in the normal manner of the host system. The IP address used
> by any guests using this interface / network based on this interface
> should be configured in the guest just as you would any other interface
> (if the guest is configured to get its IP address from DHCP, then you
> would need to have a DHCP server running *on a different host* connected
> to the .8 vlan.
>
> (BTW, note that in passthrough mode, only a single guest can connect to
> each physical device, so having a<network>  defined for passthrough mode
> is mostly only useful if you have a pool of devices available. The way
> you have it defined above, only a single guest would be able to use that
> network.)
Hi Laine,
/
/Thank you for your detailed reply!
The vdsm support bridgless network by libvirt through passthrough mode, it just
define a network by the xml format:

<network>
   <name>vdsm-XXX</name>
   <uuid>...</uuid>
   <forward dev=... mode='passthrough>
     <interface dev=.../>
   </forward>
</network>

I want to let IP address config for the host network enabled. It doesn't have to
be connected by a VLAN device,a simpler example, If I create a bridgeless
network by passthrough mode, its interface is eth0. What is the xml format for
the host to let the IP address configuration enabled?

Thanks!

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-- 
Lei

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