Re: what determines the type of virtual NIC in libvirt (veth or tap)?

Laine Stump <laine@xxxxxxxxx> · Thu, 20 Sep 2018 11:52:22 -0400



    On 09/20/2018 04:52 AM, Frank Wang
      wrote:

    
        Hi All,
        

        I'd like to know what determines the type of virtual NIC in
          libvirt ? There was a problem I encountered, the vm can't get
          the mirror traffic while the virtual port in openvswitch is
          veth, If the virtual port is tun, the everything is fine.
        

        [root@allinone-247 ~]# ethtool -i vn62f717800

          driver: veth

          version: 1.0

          firmware-version: 

          expansion-rom-version: 

          bus-info: 

          supports-statistics: yes

          supports-test: no

          supports-eeprom-access: no

          supports-register-dump: no

          supports-priv-flags: no
        

        I uninstall the veth kernel module, then restart vm, then
          the vm can receive the mirror traffic
        

        [root@allinone-247 ~]# ethtool -i vn62f717800

          driver: tun

          version: 1.6

          firmware-version: 

          expansion-rom-version: 

          bus-info: tap

          supports-statistics: no

          supports-test: no

          supports-eeprom-access: no

          supports-register-dump: no

          supports-priv-flags: no

        
        so, I'm wondering if there are configuration options which
          can be configured to use which type of virtual NIC(tap or
          veth).
        

        Any comments would be appreciate.

        
    From IRC, here is the <interface> you posted:

    
         <interface type="bridge">

           <mac address="00:16:3e:73:30:07"/>

           <source bridge="managevSwitch"/>

           <vlan>

             <tag id="0"/>

           </vlan>

           <virtualport type="openvswitch">

             <parameters
    interfaceid="8a344c7762a32b2d0162db9d09f42efa"/>

           </virtualport>

           <target dev="vnfa3b798b1"/>

           <model type="virtio"/>

           <address type="pci" domain="0x0000" bus="0x0"
    function="0x0" slot="0x11"/>

         </interface>

    
    If you are creating a qemu/kvm virtual machine, the above interface
    config will *always* get you a tap device, and if you are creating
    an LXC virtual machine it will always get you a veth device. This is
    a necessity of the way the two technologies expose the network
    device in the guest; if you are getting a veth device for use with
    qemu/kvm, or a tap device for use with LXC, then there is something
    going on that I don't understand.

  
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