[Fedora-xen] VLANs on DomU domains

[Bertho Stultiens]

Darryl Bond wrote:
> I managed to get it to work something along the lines of your first
> method before I read your email. I was also unsuccessful using your
> second method.

It still eludes me why the second method does not work, but the first
seems to be ok too. Users cannot change set setup, so there is no real
risk involved.


[snip]
> I found that if I used VLANs on the Dom0 on eth0 then the trunk would
> not pass through to the guests,  Hence why Dom0 is not using VLANs on eth0.
> I did not do much research to discover why except that the instant I
> removed the VLANs from Dom0 eth0 the VLAN networks started working on
> the guest.

You have to take care here because in Dom0 you have ethX and pethX.
Vlans on ethX(dom0) will work whereas those on peth0 apparently do not
as expected. My current setup is like this:

peth0 -> xenbr0 -> vif0.0 -> eth0(Dom0)+IP-> eth0.42+IP
                -> vif1.0 -> eth0(Guest1) -> eth0.42+IP
                -> vif2.0 -> eth0(Guest2) -> eth0.42+IP
                -> ...

Dom0 is part of vlan 42 and my management (no routing between them
enabled though). The uplink peth0 is a trunk with management untagged
and vlan 42 tagged.

My guess why the other setup has problems lies in several parts.
Firstly, the management MAC address (default fe:ff:ff:ff:ff:ff) of the
second bridge must be different. I forgot to change that and have had
problems with that before with STP enabled (bridge can otherwise not be
uniquely identified). And secondly, juggling with peth0.X can only be
done after xen has remapped the interfaces. The remapping occurs after
the original network is brought up. I need to go through the xen scripts
to get that right, I guess.

I'll have to do some more experimenting to get this pinned down because
it actually is interesting to have bridges that can swap/map/juggle vlan
tags.

-- 
Greetings Bertho


Bertho Stultiens
Senior Systems Manager
Mobilethink A/S