Re: How does the libvirt deal with the vnet mac address

Laine Stump <laine@xxxxxxxxx> · Tue, 28 Apr 2015 12:34:29 -0400



    (I'm not sure what the
      settings/commands are in the email application you use ("foxmail"
      apparently), but please configure it / use it such that you
      *reply* to messages rather than adding text onto a *forwarded*
      copy of the message you mean to reply to - in a "reply",
      everything in the original message has "> " (or something
      similar) added to the beginning of each line so that you can
      insert your own text in the middle and it will be easily
      recognizeable (no markers). Also, sending your messages in plain
      text format would be greatly appreciated (some readers of the
      mailing list will not be able to read your messages since they are
      in html-only, so you are lowering the visibility of your
      questions.)

      
      On 04/28/2015 09:48 AM, wh.h@xxxxxxxxxxx wrote:

    
    >
      I  remain puzzled about :

    
          Laine Stump wrote:

             
            > it's important to also
          > know that it is essential the tap device's MAC
            address be different from
          > the MAC address used by the guest. The reason is
            that the tap device
          > will not forward a packet to the other side of
            itself if it sees a
          > destination MAC address matching its own - it will
            think that the packet
          > must be intended for local delivery; this is another
            reason that libvirt
          > replaces the 1st byte of the guest address with 0xFE
            when setting the
          > tap device address.
        
      
          Does "the other side" mean :

            one side is ethx in the VM, the other side is tap device in the hypervisor?
          But , these two devices is
              actually the same one .  If package is received in the
              ethx device in the VM , the package also arrives at the
              tap device  in the hypervisor at the same
              time , doesn't  it ?
        
      
    Well, not exactly, but I think I replied before I had enough coffee.
    You can disregard that entire paragraph, as it was based on some old
    memory of [something, not sure what right now] and experiments I
    performed just now verified that it is *not* the case for tap
    devices.

    
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