QEMU-KVM 'Random' Virtual MAC Address.

QEMU-KVM 'Random' Virtual MAC Address.

[Veruca Salt]

Hello.
When creating an NIC in qemu, I have found that the default address on XP virtual machines is the same for two VM's on different physical boxes.
Before we go off building an assignment programme to retrofit VM's upgraded to the fit we're planning, will differently imaged VM's, with different Computer Names and other data, produce different randomised VMAC's, or will they always set to the standard default?

If they do, we are in a happier place already.

Regards,
Simon
 		 	   		  

Re: QEMU-KVM 'Random' Virtual MAC Address.

[Markus Armbruster]

Veruca Salt <verucasaltuk@hotmail.co.uk> writes:

> Hello.
> When creating an NIC in qemu, I have found that the default address on XP virtual machines is the same for two VM's on different physical boxes.
> Before we go off building an assignment programme to retrofit VM's upgraded to the fit we're planning, will differently imaged VM's, with different Computer Names and other data, produce different randomised VMAC's, or will they always set to the standard default?
>
> If they do, we are in a happier place already.

The default MAC address is 52:54:00:12:34:N, where N is 0x56 for the
first NIC, 0x57 for the second, and so forth.  Best not to rely on the
order of NIC initialization.

RE: QEMU-KVM 'Random' Virtual MAC Address.

[Veruca Salt]

Thanks Markus.
We wrote a simple app this morning which generates a random address(obviously not true GUID) which should be safe enough if a customer runs two physical boxes local-side of their network.
We are currently running a single VM on each box, with two NIC's, one dedicated to host comms across IP and one for the 'world'. Reliable and safe, the MACAddress is the last part of the jigsaw.
Bit of a step down, actually; with host Kernel 2.6.32 we were able to pass though IOMMU devices, but with Sandy Bridge having shared IRQ's on South Bridge and the 2.6.38 kernel (one of the few we can use that 'fully' works with Sandy)and the move to 64 bit, IOMMU was disastrously unstable, hence the move back to virtual taps.
Simon

----------------------------------------
> From: armbru@redhat.com
> To: verucasaltuk@hotmail.co.uk
> CC: kvm@vger.kernel.org
> Subject: Re: QEMU-KVM 'Random' Virtual MAC Address.
> Date: Wed, 2 May 2012 08:58:06 +0200
>
> Veruca Salt <verucasaltuk@hotmail.co.uk> writes:
>
> > Hello.
> > When creating an NIC in qemu, I have found that the default address on XP virtual machines is the same for two VM's on different physical boxes.
> > Before we go off building an assignment programme to retrofit VM's upgraded to the fit we're planning, will differently imaged VM's, with different Computer Names and other data, produce different randomised VMAC's, or will they always set to the standard default?
> >
> > If they do, we are in a happier place already.
>
> The default MAC address is 52:54:00:12:34:N, where N is 0x56 for the
> first NIC, 0x57 for the second, and so forth. Best not to rely on the
> order of NIC initialization.
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
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RE: QEMU-KVM 'Random' Virtual MAC Address.

[Veruca Salt]

Thanks Brian.
I've had the extra VMAC code in the boot line for months. I guess I'll have to patch it in with a script that assigns individual host config file variables. Not too difficult.'Write' script and MACAddress database.
Simon
________________________________
> Date: Tue, 1 May 2012 23:07:40 -0500 
> Subject: Re: QEMU-KVM 'Random' Virtual MAC Address. 
> From: iggy@theiggy.com 
> To: verucasaltuk@hotmail.co.uk; kvm@vger.kernel.org 
>  
> Qemu uses the same mac even if you start 2 guests on the same host. The  
> different processes have absolutely no idea about each other so they  
> couldn't communicate that the default is used already. And per startup  
> random macs is a bad idea because guests will think you are constantly  
> changing hardware. This is usually handled by the mgmt layer (libvirt,  
> etc). If you are managing your own VMs, your best bet is to build it in  
> to your script/daemon/etc. 
>  
>  
>  
>  
> Veruca Salt <verucasaltuk@hotmail.co.uk> wrote: 
>  
>  
>  
>  
> Hello. 
> When creating an NIC in qemu, I have found that the default address on  
> XP virtual machines is the same for two VM's on different physical  
> boxes. 
> Before we go off building an assignment programme to retrofit VM's  
> upgraded to the fit we're planning, will differently imaged VM's, with  
> different Computer Names and other data, produce different randomised  
> VMAC's, or will they always set to the standard default? 
>  
> If they do, we are in a happier place already. 
>  
> Regards, 
> Simon 
>       -- 
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