macvtap direct

[Subhendu Ghosh]

On Thu, May 14, 2020 at 1:32 PM Laine Stump <laine at redhat.com> wrote:

> On 5/13/20 12:52 AM, Subhendu Ghosh wrote:
> > Hi
> >
> > Couple of questions around macvtap direct usage:
> >
> > 1) is the document here current?
> > https://libvirt.org/formatnetwork.html#examplesDirect
>
> Yes. None of that has changed in any major way in many years.
>

kernelNewbies documents mactap bridge as VMs can host can all talk to each
other without an external bridge
External bridge/switch is only needed for VEPA mode with hairpin.

https://virt.kernelnewbies.org/MacVTap

Perhaps the original development of macvtap to support VEPA influenced the
early docs and was never reviewed after bridge mode matured?



> >
> > I have been able to get host to guest network traffic without any
> > special configuration or switch since Fedora 28 when I first started
> > using it. Using <forward mode=vepa> requires switch port mirroring, but
> > just using <forward mode=bridge> doesn't.
>
>
> If that is the case, then either your guest and host have a secondary
> network connection, or your switch is mirroring traffic and you just
> didn't know about it. The inability to do direct host<->guest
> communication is inherent in the design of macvtap interfaces.
>
>
> >
> > 2) do any of the language libraries make assumptions that libvirt
> > networks must have a <bridge name=xx> attribute? Foreman's Ruby
> > interface to libvirt errors out with attempting to build a VM on a KVM
> > host with a network defined with <forward mode=bridge>
> > https://projects.theforeman.org/issues/25890
>
> The 2nd line in the log attached to that issue report says this:
>
>  >Call to virNetworkGetBridgeName failed: internal error: network
> 'macvtap-net' does not have a bridge name.
>
> So, your application (or whatever this "Foreman's Ruby interface to
> libvirt" is) has called virNetworkGetBridgeName() (whatever it's called
> in the Ruby bindings), and since you have a macvtap network, which has
> no bridge device, libvirt sent back an error. You need to find whatever
> in your code is calling virNetworkGetBridgeName().
>
>
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