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

Sent: Tuesday, May 01, 2018 at 5:30 PM From: "Laine Stump" <laine(a)redhat.com&gt; To: libvirt-users(a)redhat.com Cc: daggs <daggs(a)gmx.com&gt; 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(a)redhat.com&gt; >> To: libvirt-users(a)redhat.com >> Cc: daggs <daggs(a)gmx.com&gt; >> 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...)