[libvirt-users] connecting host and guest vm using a dummy nic

Mon Apr 30 19:16:22 UTC 2018

Greetings Laine,

> Sent: Monday, April 30, 2018 at 8:31 PM
> From: "Laine Stump" <laine at redhat.com>
> To: libvirt-users at redhat.com
> Cc: daggs <daggs at gmx.com>
> Subject: Re: [libvirt-users] connecting host and guest vm using a dummy nic
>
> On 04/27/2018 06:39 PM, daggs wrote:
> > Greetings all,
> > 
> > I have a host machine that runs a router within a vm.
> > I want to allow a connection between the host and the guest so the host can connect to the lan provided by the router vm.
> > I've created a dummy interface with these commands:
> > $ ip link add ens99-dummy type dummy
> > $ ip link set ens99-dummy address 52:54:00:1f:d0:ff
> > 
> > this resulted with this output:
> > $ ifconfig ens99-dummy
> > ens99-dummy Link encap:Ethernet  HWaddr 52:54:00:1F:D0:FF 
> >           inet6 addr: fe80::84b5:24ff:fe62:c16d/64 Scope:Link
> >           UP BROADCAST RUNNING NOARP  MTU:1500  Metric:1
> >           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> >           TX packets:899 errors:0 dropped:0 overruns:0 carrier:0
> >           collisions:0 txqueuelen:1000
> >           RX bytes:0 (0.0 B)  TX bytes:321727 (314.1 KiB)
> > 
> > 
> > in my libvirt's xml file I have this entry:
> >     <interface type='direct'>
> >       <mac address='52:54:00:0c:cb:3e'/>
> >       <source dev='ens99-dummy' mode='private'/>
> >       <target dev='macvtap0'/>
> >       <model type='e1000'/>
> >       <alias name='net0'/>
> >       <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
> >     </interface>
> 
> MY first question would be "Why are you using macvtap?" This
> unnecessarily complicates the plumbing, leading to more potential places
> where it could fail.
misconfiguration, question is, what should be the exact config for this.

> 
> The 2nd question is - Have you looked at the dhcp server running on the
> guest to verify that it is indeed listening for DHCP requests on the
> guest-side interface associated with the macvtap interface, and that it
> is receiving those requests and sending a reply?
will test it. as said before, I'm not sure what should be the proper config in libvirt.

> 
> > 
> > after the vm is up, I see the adapter in the vm and the host has one more entry:
> > $ ifconfig macvtap0
> > macvtap0  Link encap:Ethernet  HWaddr 52:54:00:0C:CB:3E 
> >           inet6 addr: fe80::5054:ff:fe0c:cb3e/64 Scope:Link
> >           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
> >           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> >           TX packets:889 errors:0 dropped:0 overruns:0 carrier:0
> >           collisions:0 txqueuelen:500
> >           RX bytes:0 (0.0 B)  TX bytes:320523 (313.0 KiB)
> > 
> > but when I try to request ip via dhcp from both macvtap0 and ens99-dummy I don't get any.
> > any idea why?
> 
> Definitely you wouldn't be able to use the macvtap0 device, so if
> anything you would want to be using ens99-dummy, but I'm not even
> certain *that* would work, as I've never tried it.
so use ens99-dummy directly? 

> 
> You've provided no visibility into the configuration of the guest OS in
> your virtual machine, but in general if you want a simple connection
> between the host and guest that has *no other connections*, you can do
> this with a bare tap device:
> 
>     <interface type='ethernet'>
>       <model type='e1000'/>
>     </interface>
> 
> This will show up as a single device on the host and a single device in
> the guest, not connected to a bridge or a macvtap device or anything,
> and will not need any other "ip link blah blah" type setup on the host.
> Simplifying your setup in this manner may make it easier to find the
> source of your problem.
> 

ok, here is the entire xml file:

<domain type='kvm'>
  <name>router</name>
  <uuid>ed8eabe2-ced3-4224-aa12-60fb31dd3fd4</uuid>
  <memory unit='KiB'>1048576</memory>
  <currentMemory unit='KiB'>1048576</currentMemory>
  <vcpu placement='static'>2</vcpu>
  <os>
    <type arch='x86_64' machine='pc-q35-2.8'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cpu mode='host-passthrough'/>
  <clock offset='utc'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <pm>
    <suspend-to-mem enabled='no'/>
    <suspend-to-disk enabled='no'/>
  </pm>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/home/router/lede-x86-64-combined-ext4.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x2'/>
    </controller>
    <controller type='sata' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pcie-root'/>
    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
      <model name='i82801b11-bridge'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1e' function='0x0'/>
    </controller>
    <controller type='pci' index='2' model='pci-bridge'>
      <model name='pci-bridge'/>
      <target chassisNr='2'/>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
    </controller>
    <controller type='pci' index='3' model='pcie-root-port'>
      <model name='ioh3420'/>
      <target chassis='3' port='0x8'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/>
    </controller>
    <controller type='pci' index='4' model='pcie-root-port'>
      <model name='ioh3420'/>
      <target chassis='4' port='0x9'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <controller type='pci' index='5' model='pcie-root-port'>
      <model name='ioh3420'/>
      <target chassis='5' port='0xa'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='pci' index='6' model='pcie-root-port'>
      <model name='ioh3420'/>
      <target chassis='6' port='0xb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x3'/>
    </controller>
    <controller type='pci' index='7' model='pcie-root-port'>
      <model name='ioh3420'/>
      <target chassis='7' port='0xc'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x4'/>
    </controller>
    <controller type='pci' index='8' model='pcie-root-port'>
      <model name='ioh3420'/>
      <target chassis='8' port='0xd'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x5'/>
    </controller>
    <interface type='direct'>
      <mac address='52:54:00:e7:90:bc'/>
      <source dev='ens99-dummy' mode='vepa'/>
      <model type='rtl8139'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target type='isa-serial' port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x148f'/>
        <product id='0x5572'/>
      </source>
      <address type='usb' bus='0' port='1'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
    </hostdev>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </memballoon>
  </devices>
</domain>

what I don't get is how to connect the interface above to the dummy one I've created.