libvirt users - May 2018 - Re: connecting host and guest vm using a dummy nic

Greetings Laine,
> Sent: Wednesday, May 02, 2018 at 8:09 PM
> From: "Laine Stump" <laine@redhat.com>
> To: libvirt-users@redhat.com
> Cc: daggs <daggs@gmx.com>
> Subject: Re: [libvirt-users] connecting host and guest vm using a dummy nic
>
> On 05/02/2018 12:05 PM, daggs wrote:
> > Greetings Laine,
> > 
> >> Sent: Wednesday, May 02, 2018 at 5:56 PM
> >> From: "Laine Stump" <laine@redhat.com>
> >> To: libvirt-users@redhat.com
> >> Cc: daggs <daggs@gmx.com>
> >> Subject: Re: [libvirt-users] connecting host and guest vm using a
dummy nic
> >>
> >> On 05/01/2018 12:12 PM, daggs wrote:
> >>>
> >>> I want to see if I understood you correctly, I add:
> >>> <interface type='ethernet'>
> >>>    <model type='e1000'/>
> >>> </interface>
> >>> to the vm's xml, this will result in a new nic in the vm
which and in the host which I can use by the host to request dhcp from the
router within the vm?
> >>>
> >>
> >>
> >> Yes. As long as the emulated device in the guest is listening for
DHCP
> >> on that interface.
> >>
> >> Also, note that (as long as your libvirt is at least version
2.1.0) if
> >> you don't want to bother doing dhcp on the host and guest, you
can
> >> assign just a static IP address for the host side of that
interface in
> >> the libvirt XML like this:
> >>
> >>
> >>   <interface type='ethernet'>
> >>     <source>
> >>        <ip address='192.168.254.2'/>
> >>     </source>
> >>     ...
> >>
> >> You can even specify routes to be added automatically to the host
when
> >> that guest is started, e.g.:
> >>
> >>
> >>   <interface type='ethernet'>
> >>     <source>
> >>        <ip address='192.168.254.2'/>
> >>        <route family='ipv4' address='0.0.0.0'
prefix='0'
> >>               gateway='192.168.254.1'
metric='1'/>
> >>     </source>
> >>     ...
> >>
> >> (this assumes that on the guest side, the OS has configured the
emulated
> >> ethernet device to have address 192.168.254.1). This can be useful
if
> >> you want the host to use one path for traffic when the guest
isn't
> >> running, but switch when the guest *is* running. (In this case, if
you
> >> can set the default route on the host to have a metric of 2 or
higher,
> >> then the default route that goes through the guest would be
preferred
> >> when present).
> >>
> >> (NB: if you read the documentation for configuring interfaces at
> >> https://libvirt.org/formatdomain.html#ipconfig you'll see
references on
> >> how to configure the IP address of the *guest* in libvirt's
xml. Note
> >> that this *does not work* for qemu, but only for lxc (and possibly
xen,
> >> I don't recall right now). This is a limitation of the way
that qemu/kvm
> >> works (the fact that all guest-side IP info is configured in the
guest
> >> OS, and libvirt has no reasonable to get to it).)
> >>
> >>
> > 
> > thanks alot!
> > like you've said, I've defined the interface in the xml,
booted the device and updated /etc/network/interfaces to alloc dhcp to vnet0.
> > that resulted in the proper ip and I can see the router inside the vm.
> 
> BTW, if you'll be running other guests on your host, and may start them
> in different orders, you should probably add "<target
dev='vmrouter'/>
> (or whatever name you like, 15 chars or less and *not* starting with
> "vnet") to the <interface> config. IF you do that, you can
be assured
> that the name of the device on the host will always be consistently
> named "vmrouter" (otherwise it just gets the lowest numbered
available
> "vnetX" device name each time it's started).
> 
I intend to run only one vm on this system, thanks for the tip.
> 
> > 
> > one thing bothers me, ethtool vnet0 says the speed is 10Mb/s, asking
google suggested several solutions.
> > I've tried changing the model to virtio but the speed stays the
same, the vm router is running kernel 4.4.92, could that be the issue?
> 
> The reported speed should be inconsequential, since there is no wire and
> no physical switch involved. It will transfer data as fast as the code
> can be executed.
> 
> Also, if virtio works, then *definitely* use that instead of e1000 - the
> performance will be much better and overhead much lower.
> 
> 
so any network test will do?

Thanks, 

Dagg.

On 05/02/2018 01:28 PM, daggs wrote:
>> Sent: Wednesday, May 02, 2018 at 8:09 PM
>> From: "Laine Stump" <laine@redhat.com>
>>
>> Also, if virtio works, then *definitely* use that instead of e1000 -
the
>> performance will be much better and overhead much lower.
>>
>>
> so any network test will do?
> 

Do you mean to test and see if virtio-net is acceptable for your guest
OS? If the guest OS has the driver for virtio-net, then definitely you
should use it. I've never heard of a case of any of the drivers that
emulate real hardware performing anywhere near as well as virtio-net.

Greetings Laine,
> Sent: Thursday, May 03, 2018 at 1:13 AM
> From: "Laine Stump" <laine@redhat.com>
> To: libvirt-users@redhat.com
> Cc: daggs <daggs@gmx.com>
> Subject: Re: [libvirt-users] connecting host and guest vm using a dummy nic
>
> On 05/02/2018 01:28 PM, daggs wrote:
> 
> >> Sent: Wednesday, May 02, 2018 at 8:09 PM
> >> From: "Laine Stump" <laine@redhat.com>
> 
> >>
> >> Also, if virtio works, then *definitely* use that instead of e1000
- the
> >> performance will be much better and overhead much lower.
> >>
> >>
> > so any network test will do?
> > 
> 
> 
> Do you mean to test and see if virtio-net is acceptable for your guest
> OS? If the guest OS has the driver for virtio-net, then definitely you
> should use it. I've never heard of a case of any of the drivers that
> emulate real hardware performing anywhere near as well as virtio-net.
> 
no, I mean test the virtual nic speed, will ipref work?
also, in the guest os, the module attached to the virtual nic is virtio-pci, is
that expected?