[libvirt-users] connecting host and guest vm using a dummy nic
Laine Stump
laine at redhat.com
Tue May 1 14:30:59 UTC 2018
On 04/30/2018 03:16 PM, daggs wrote:
> 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?
My suggestion is to scrap the idea of using macvtap and a dummy link
entirely, and just use a plain tap device. I can't think of any reason
why you would want to use macvtap rather than tap in this case
>
>>
>> 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:
like this:
>>
>> <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:
(I actually meant the network configuration within the guest OS, not the
libvirt config of the virtual machine it's running on)
>
> <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.
>
That's easy. Don't - see my suggestion above about using a tap device
instead of the macvtap+dummy combination (actually, I had thought the
"<source dev='ens99-dummy' ..." should connect the two, but according to
your experiments that doesn't result in a working setup, so...)
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