[ovirt-users] Guest PXE boot with 2 NICs : MAC order

[Lior Vernia]

On 31/03/15 15:34, Nicolas Ecarnot wrote:
> Le 31/03/2015 13:57, Lior Vernia a écrit :
>>
>>
>> On 31/03/15 14:21, Nicolas Ecarnot wrote:
>>> Hi Lior,
>>>
>>> Le 31/03/2015 12:55, Lior Vernia a écrit :
>>>> Indeed, if you're using oVirt 3.4 and up, and you supply all the NICs
>>>> whenever you create the VM (not afterwards - as part of the new VM
>>>> dialog), the NICs should receive MAC addresses according to their
>>>> ordering by names, e.g. nic1 will always get a lower MAC address than
>>>> nic2. For a newly-created VM this should guarantee that nic1 will
>>>> indeed
>>>> end up the first NIC inside the guest OS and be used by PXE.
>>>
>>> In the BZ I provided above, I explain that my tests are showing that
>>> this is not true : the nics are not yet sorted according to their MAC
>>> nor their names.
>>>
>>> I'm using 3.5.1
>>>
>>
>> I see. It seems MAC addresses are allocated according to the NIC name
>> order,
> 
> I'm not sure this is exact.
> According to what I'm witnessing, MAC addresses are allocated in
> incremental order, from the first free MAC address in the MAC pool range.
> 

My question is as follows: when you create a VM, and add NICs as part of
the new VM dialog (using the widget at the bottom), have you ever
encountered a situation where a "higher-named" NIC got a lower MAC address?

>> and that they are also named in the corresponding order within
>> the guest OS.
> 
> Er.. what gives when I'm naming my interfaces ethX, and amongst that,
> oVirt comes trying to add some nicX???
> 

When NICs are added *after* the VM had already been created, it really
depends whether the VM is currently running and they're being hotplugged
or whether it's not running, and also on the guest OS (this last bit is
always true).

If the VM is running and NICs are being hotplugged as soon as they're
created, I'd expect them to receive "increasing" names within the guest
OS according to the order of creation, regardless of MAC address (at
least if we're talking about newer RHEL and Fedora versions).

>> So the only problem here is how gPXE chooses a NIC to boot
>> from... I'm not familiar with the behavior of gPXE, but oVirt seems to
>> behave alright.
> 
> I mostly agree with that, in the sense that one has to dig in which way
> gPXE is sorting the NICs, ie mapping the MACs to its "net0", "net1", and
> so on.
> 

That's the key point here for me, as it's difficult to predict the
behavior of n'importe quel piece of software... :)

> And then, decide whether oVirt could have a control upon this sorting,
> and then issue a RFE to master it from the web GUI.
>