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

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>

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?

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.

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?
> 
> 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.

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.

Greetings Laine,
> Sent: Monday, April 30, 2018 at 8:31 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 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.