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Re: Xen3 + VLANs + multiple DOM0s cause loss of connectivity?

Hi Manuel,

On 24 Jan 2008, at 15:58, Manuel Bouyer wrote:

Outside of VLANs (i.e. when configuring IPv4 and IPv6 addresses
directly on the xennetN then everything works just fine. VLANs
configured on the DOM0 also works fine. It is just the combination of
Xen3 + DOMU + VLANs that causes problems.

What I found strange is that it worked with Xen2. Xen version is probably
not the key here, but the version of dom0.

Basically, 802.1q paquets in dom0 are not routed to the bridge interface but to the vlan interfaces, so these packets can't make it up to the domUs.

Umm. There is confusion here, probably mine. I have lots of 802.1q packets that go just fine across the bridge interface between DOMUs in the same DOM0, and they most certainly make it up to the DOMUs. What the packets don't do is go across the physical switch (between DOM0s) that the DOM0 bridge device is connected to. So I have to challenge the assertion that the packets are not routed to the DOM0 bridge interface.

If the dom0 kernel doesn't have 'pseudo-device vlan' then it may work.

I'll try that ASAP, but that will not be until next week when I get home (presently on the lower half of the planet).

The way to do this is to have the vlan interfaces in dom0 only, connect one bridge to each vlan and have in the domU one vif per vlan you need to
connect to.

Doesn't work for me as I need to be able to dynamically affect topology from inside the DOMUs. I.e. I implement nomadic behaviour by having DOMUs change their VLAN tag. And on occasion I have several dozen VLANs. There's no way I can do that with bridges and bunches of xennets.

I remember discussing this with you at a previous occasion when I was trying to have communication between the DOM0(s) and the DOMUs over VLANs (with very limeted success). You explained that the DOM0 couldn't do the right thing wrt to both dealing with bridges and vlan interfaces and therefore VLANs on the DOM0 would not see the traffic arriving on the same VLAN from a DOMU (i.e. the bridge gets the packet, not the DOM0 vlan interface). As a consequence of that I stopped using VLANs entirely on the DOM0s and moved all services into yet another DOMU and that has worked just fine for a long time.

But now, if I understand correctly, you're saying that in the conflict between sending the packet to the VLAN or to the bridge the VLAN gets the packet. That sounds completely contrary to what you said before and not at all in line with my experience.



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