Re: vifs not working?

[Sarton O'Brien <bsd-xen%roguewrt.org@localhost>]

der Mouse wrote:
> > I guess my thought is, without an ethernet device nor a bridge, how
> > is a vif to communicate?  What exactly are you pinging?
>
> The dom0 and the domU communicate with one another.
>
> dom0# ifconfig vif3.0 10.1.0.1/24
> domU# ifconfig xennet0 10.1.0.2/24
> dom0# ping 10.1.0.2
> ...works...
> domU# ping 10.1.0.1
> ...works...
>
> The documentation says that the xennet interface and the vif interface
> are effectively like a crossover cable between two Ethernet ports.
> Except for the issue that they don't stay around because the "hotplug
> scripts", whatever they are, aren't working, that's exactly how they
> seem to be behaving.

I didn't realise that. I had assumed the vifs were independent and had 
to be bound to something. In that case it seems quite plausible they 
should function as you expect, maybe it's just an untested scenario ...

> > > I don't see what PCI access has to do with it; nothing says there's
> > > a PCI bus anywhere in sight.
> > No ... but if you were to opt out of a bridge, then you'd usually
> > choose a physical interface.  Unless there is some other way to
> > emulate the physical layer that I'm unaware of (quite possibly).
>
> I don't see why you'd need to.  The xennet interface in the domU seems
> to communicate with its corresponding vif interface in the dom0 just
> fine.  Whether the vif interface happens to be a member of a bridge is,
> as far as I can see, entirely orthogonal to this - or, at least, it
> should be; I can't see why a vif being a member of a bridge would
> matter to anything.

It's highly likely that it doesn't matter. As stated, I haven't ventured 
much outside standard config and can only identify differences in yours. 
From what I've seen on the list, most people expose their domus and 
apply vlan tagging using dom0 as router. Yours may be a considerably 
less tested scenario.

> The whole auto-bridging thing seems to be built around the assumption
> that you want the domUs and the dom0 to, effectively, share a physical
> interface.  If you do, this is fine, but if you don't - if you'd rather
> have the domUs form one or more small private networks with the dom0 as
> a router between them and the real network, or if you don't want the
> domUs to communicate with anything beyond the dom0 - I can't see why
> that should be a problem.

No it probably shouldn't. Hopefully this is something Manuel has tested 
and can respond to. Alternatively, anyone else have this type of setup?

> > The bridge is merely required to emulate the use of a physical
> > interface.
>
> I don't see why.  The xennet/vif pair seems to emulate two physical
> interfaces connected to one another just fine.  If I happen to want to
> bridge a vif with a real interface, great, but I can't see any reason I
> should have to if I'd rather not.

Well I was clearly wrong, see above. Your problem may not have anything 
to do with bridging what-so-ever ... but as it's the one exception in 
our configs, maybe it's worth trying to isolate the problem a little 
bit? At the least, if it doesn't work then it's highly likely a bug.

Sarton