Mac-Address uniqueness

Mac-Address uniqueness

[Axel Kittenberger]

Hello List!

Im not sure if this better kvm or qemu code that is responsible, but 
since my binary is called "kvm" I'll try this list first, tell me if its 
wrong.

I now have 3 virtual machines on my host (Windows 2003 server, Ubuntu 
etch, an old Suse) and have bridged networking setup.
I used -nic,model=rtl8139 on all machines, maybe because Windows needed 
it, and then I just kept my script...

Unfortunally all machines detect the same ethernet address 
'52:54:00:12:34:56'. Which you can guess what i means, networking comes 
and goes whatever machine last the ethernet address got hold of from the 
gateway. I tried specifing an ethernet-adress with "-net 
nic,macaddr=$MAC" but this also didn't work through.

For now I just hardseted the mac in all machines to 52:54:00:12:34:57, 
52:54:00:12:34:58 and so on.

Greetings, Axel

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Re: Mac-Address uniqueness

[Dor Laor]

>Im not sure if this better kvm or qemu code that is responsible, but
>since my binary is called "kvm" I'll try this list first, tell me if
its
>wrong.
>
>I now have 3 virtual machines on my host (Windows 2003 server, Ubuntu
>etch, an old Suse) and have bridged networking setup.
>I used -nic,model=rtl8139 on all machines, maybe because Windows needed
>it, and then I just kept my script...
>
>Unfortunally all machines detect the same ethernet address
>'52:54:00:12:34:56'. Which you can guess what i means, networking comes
>and goes whatever machine last the ethernet address got hold of from
the
>gateway. I tried specifing an ethernet-adress with "-net
>nic,macaddr=$MAC" but this also didn't work through.
>
>For now I just hardseted the mac in all machines to 52:54:00:12:34:57,
>52:54:00:12:34:58 and so on.

It works for me.
You should have all the -nic parameters in the same option, for example:
"-net nic,macaddr=$MAC,model=rtl8139" otherwise qemu sets the nic for
another vlan object.

>
>Greetings, Axel
>
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Re: Mac-Address uniqueness

[Axel Kittenberger]

Thanks for the quick answer.
> It works for me.
> You should have all the -nic parameters in the same option, for example:
> "-net nic,macaddr=$MAC,model=rtl8139" otherwise qemu sets the nic for
> another vlan object.
>   
Oh! This explains why lspci showed 3 network cards, stupid me :-)
Still specifing a macaddr, will make the interface not work for me in a 
debian-40r0-i386 host! :-(

So the whole commandline im using is:
/usr/local/bin/kvm-helios -hda /home/machines/helios.img -vnc :1 -boot 
c: -m 1024 -net nic,model=rtl8139,vlan=0,macaddr=52:54:00:12:34:59 -net 
tap,vlan=0,ifname=tap57,script=/etc/qemu-ifup-dmz -localtime -k de 
-pidfile /var/run/kvm-helios.pid

After bootup with macaddr set, the debian system does not autoload any 
modules for eth0.
Attached some response to shell commands:
---------------------------
helios# lspci
00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE 
[Natoma/Triton II]
00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI
00:02.0 VGA compatible controller: Cirrus Logic GD 5446
00:03.0 Ethernet controller: Realtek Semiconductor Co., Ltd. 
RTL-8139/8139C/8139C+ (rev 20)
helios# modprobe 8139cp
May 31 16:03:43 helios kernel: 8139cp: 10/100 PCI Ethernet driver v1.2 
(Mar 22, 2004)
May 31 16:03:43 helios kernel: PCI: Enabling device 0000:00:03.0 (0000 
-> 0003)
May 31 16:03:43 helios kernel: ACPI: PCI Interrupt 0000:00:03.0[A] -> 
Link [LNKC] -> GSI 10 (level, low) -> IRQ 10
May 31 16:03:43 helios kernel: eth0: RTL-8139C+ at 0xf883c000, 
52:54:00:12:34:59, IRQ 10
helios# ifconfig eth0
eth0: error fetching interface information: Device not found
---------------------------
While same kvm-parameters but without setting maccdr  with setting the 
macaddr debian autoloads it: (excerpt from /var/log/messages)
---------------------------
May 31 16:06:01 helios kernel: 8139too 0000:00:03.0: This (id 10ec:8139 
rev 20) is an enhanced 8139C+ chip
May 31 16:06:01 helios kernel: 8139too 0000:00:03.0: Use the "8139cp" 
driver for improved performance and stability.
May 31 16:06:01 helios kernel: ACPI: PCI Interrupt Link [LNKC] enabled 
at IRQ 10
May 31 16:06:01 helios kernel: ACPI: PCI Interrupt 0000:00:03.0[A] -> 
Link [LNKC] -> GSI 10 (level, low) -> IRQ 10
May 31 16:06:01 helios kernel: eth0: RealTek RTL8139 at 0xc100, 
52:54:00:12:34:56, IRQ 10
May 31 16:06:01 helios kernel: 8139cp: 10/100 PCI Ethernet driver v1.2 
(Mar 22, 2004)
---------------------------

PS: Beside I actually would be supposed to know it, and suppose setting 
macaddr would work for me, can or can't I use the macaddr linux assigns 
to the 'tap' device?

Kind Regards, Axel



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Re: Mac-Address uniqueness

[H. Peter Anvin]

Axel Kittenberger wrote:
> 
> Unfortunally all machines detect the same ethernet address 
> '52:54:00:12:34:56'. Which you can guess what i means, networking comes 
> and goes whatever machine last the ethernet address got hold of from the 
> gateway. I tried specifing an ethernet-adress with "-net 
> nic,macaddr=$MAC" but this also didn't work through.
> 
> For now I just hardseted the mac in all machines to 52:54:00:12:34:57, 
> 52:54:00:12:34:58 and so on.
> 

This is a Qemuism.  I always thought it was dumb, but I guess Qemu
wanted reproducibility over everything.

IMNSHO it would have been much better to default to a random value
(meaning that all except the bottom 2 bits of the first octet are
random, those bits should be set to 10 binary.)

	-hpa

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Re: Mac-Address uniqueness

[Avi Kivity]

H. Peter Anvin wrote:
> Axel Kittenberger wrote:
>   
>> Unfortunally all machines detect the same ethernet address 
>> '52:54:00:12:34:56'. Which you can guess what i means, networking comes 
>> and goes whatever machine last the ethernet address got hold of from the 
>> gateway. I tried specifing an ethernet-adress with "-net 
>> nic,macaddr=$MAC" but this also didn't work through.
>>
>> For now I just hardseted the mac in all machines to 52:54:00:12:34:57, 
>> 52:54:00:12:34:58 and so on.
>>
>>     
>
> This is a Qemuism.  I always thought it was dumb, but I guess Qemu
> wanted reproducibility over everything.
>
> IMNSHO it would have been much better to default to a random value
> (meaning that all except the bottom 2 bits of the first octet are
> random, those bits should be set to 10 binary.)
>
>   

That tends to consume dhcp leases quickly, if you start guests often (as
I do).  Also, some distributions use the mac address as a key for naming
interfaces; if it changes, the guest gets confused


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: Mac-Address uniqueness

[H. Peter Anvin]

Avi Kivity wrote:
> H. Peter Anvin wrote:
>> Axel Kittenberger wrote:
>>   
>>> Unfortunally all machines detect the same ethernet address 
>>> '52:54:00:12:34:56'. Which you can guess what i means, networking comes 
>>> and goes whatever machine last the ethernet address got hold of from the 
>>> gateway. I tried specifing an ethernet-adress with "-net 
>>> nic,macaddr=$MAC" but this also didn't work through.
>>>
>>> For now I just hardseted the mac in all machines to 52:54:00:12:34:57, 
>>> 52:54:00:12:34:58 and so on.
>>>
>>>     
>> This is a Qemuism.  I always thought it was dumb, but I guess Qemu
>> wanted reproducibility over everything.
>>
>> IMNSHO it would have been much better to default to a random value
>> (meaning that all except the bottom 2 bits of the first octet are
>> random, those bits should be set to 10 binary.)
>>
>>   
> 
> That tends to consume dhcp leases quickly, if you start guests often (as
> I do).  Also, some distributions use the mac address as a key for naming
> interfaces; if it changes, the guest gets confused
> 

The right solution to that, of course, is a VM definitions file, so the
random Ethernet address is only generated once.  For Qemu/KVM, that
could at least in theory simply be a shell script.

	-hpa

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Re: Mac-Address uniqueness

[Daniel P. Berrange]

On Thu, May 31, 2007 at 11:43:43PM -0700, H. Peter Anvin wrote:
> Avi Kivity wrote:
> > H. Peter Anvin wrote:
> >> Axel Kittenberger wrote:
> >>   
> >>> Unfortunally all machines detect the same ethernet address 
> >>> '52:54:00:12:34:56'. Which you can guess what i means, networking comes 
> >>> and goes whatever machine last the ethernet address got hold of from the 
> >>> gateway. I tried specifing an ethernet-adress with "-net 
> >>> nic,macaddr=$MAC" but this also didn't work through.
> >>>
> >>> For now I just hardseted the mac in all machines to 52:54:00:12:34:57, 
> >>> 52:54:00:12:34:58 and so on.
> >>>
> >>>     
> >> This is a Qemuism.  I always thought it was dumb, but I guess Qemu
> >> wanted reproducibility over everything.
> >>
> >> IMNSHO it would have been much better to default to a random value
> >> (meaning that all except the bottom 2 bits of the first octet are
> >> random, those bits should be set to 10 binary.)
> >>
> >>   
> > 
> > That tends to consume dhcp leases quickly, if you start guests often (as
> > I do).  Also, some distributions use the mac address as a key for naming
> > interfaces; if it changes, the guest gets confused
> > 
> 
> The right solution to that, of course, is a VM definitions file, so the
> random Ethernet address is only generated once.  For Qemu/KVM, that
> could at least in theory simply be a shell script.

This is the approach we use in libvirt. If the user defines a guest and
does not provide a mac address, we generate one for each NIC and store
it in the config file, so every time it gets the same MAC. 

Dan.
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Re: Mac-Address uniqueness

[Axel Kittenberger]

> That tends to consume dhcp leases quickly, if you start guests often (as
> I do).  Also, some distributions use the mac address as a key for naming
> interfaces; if it changes, the guest gets confused
>   

Couldn't we do some sort of hash on the image path+filename? So same 
image starts always with same MAC, different images -> different mac 
adresses. I guess I am supposed to post this suggestion on the qemu 
mailinglist. ;-)

- Axel

PS: Other topic, I still wonder how a guest can bevahe totally different 
on networking (unable to use network) when macaddr is set by kvm 
parameters? For me this sounds like a bug, not?

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