[libvirt] Different VLAN IDs

[Csom Gyula]

We messed up things:(

1. Unfortunately I was misinformed. In fact the problem was triggered by 
assigning the same VLAN ID-s within an SMP guest. Just as in the case 
discussed in the KVM list, it was simply resolved by assigning unique
ids within the guest.

2. After all I unit tested the other case (different guests sharing the 
same VLAN ID) and found no problem. It just works, needs no resolution.

Again thanks for the clarifications and
sorry for the mistake,

Cheers,
Gyula

-----Eredeti üzenet-----
Feladó: libvir-list-bounces at redhat.com meghatalmazó: Csom Gyula
Küldve: 2010. 05. 19., Sze 17:00
Címzett: libvir-list at redhat.com
Tárgy: Re: [libvirt] Different VLAN IDs
 
Thanks for your response!

I didn't know that VLAN IDs are internal to the individual KVM/QEMU 
processes. In fact the VLAN IDs were different within our guests. So 
it was not a perfect match...

Meanwhile the question remains, why their solution did work in our 
case. But this one should goe to the KVM/QEMU developer list..., I 
guess:)

Cheers,
Gyula

-----Eredeti üzenet-----
Feladó: Daniel P. Berrange [mailto:berrange at redhat.com]
Küldve: 2010. 05. 19., Sze 16:24
Címzett: Csom Gyula
Másolatot kap: libvir-list at redhat.com
Tárgy: Re: [libvirt] Different VLAN IDs
 
On Wed, May 19, 2010 at 04:11:36PM +0200, Csom Gyula wrote:
> Hi there,
> 
> We experienced network problems (namely net packet storm), when using multiple NICs and 
> the same VLAN ID-s for different KVM guests. It turned out that we could workaround the 
> problem by simply assigning different VLAN ID-s to the different NICs. (Btw our case 
> looked similar to the one that was posted and discussed on the KVM mailing list. Also the
> solution was picked from that discussion. See: http://www.mail-archive.com/kvm@vger.kernel.org/msg24203.html, for details)

That thread is discussing the case of 1 guest with 2 NICs, both connected 
to the same bridge on the host, thus creating a network loop between the 
guest & the host.  The VLAN ID is a QEMU internal identifier / concept 
(not related to 802.11 VLANs), that doesn't propagate to the outside world. 
So in your scenario of having multiple guests, there is no association 
between the VLAN ids in each guest's NIC.

> My questions: 
> 
>   - Did anyone experience similar problems, and come up with a clean solution? Specially 
>     is there any better way to provide unique VLAN ID-s thru libvirt then the above
>     one? 
> 
> As far as I see the upcoming -netdev option (introduced in QEMU 0.12) will solve the 
> question. However this was removed from libvirt, since the corresponding qemu monitor command 
> is not yet developed: 
> 
>   - Do you have a target release for the -netdev option, or is it unknown (eg. dependent 
>     on the yet unknown KVM/QEMU development schedule)?

It will be enabled when 0.13 QEMU comes out.


> 
> Cheers,
> Gyula
> 
> Ps.: our env: Debian GNU/Linux, libvirt, kvm, ebtables
> 
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