[libvirt-users] connecting host and guest vm using a dummy nic
daggs
daggs at gmx.com
Tue May 1 16:12:22 UTC 2018
Greetings Laine,
> Sent: Tuesday, May 01, 2018 at 5:30 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 04/30/2018 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...)
>
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?
Thanks,
Dagg.
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