[libvirt-users] How does the libvirt deal with the vnet mac address

[Laine Stump]

(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 at foxmail.com 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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