[libvirt] macvtap - no incoming ipv6 traffic processed on kvm host unless i start tcpdump on interface

Stefan Bauer sb at plzk.de
Thu Apr 9 08:39:56 UTC 2015

On Thu, 2015-04-09 at 10:12 +0200, Michal Privoznik wrote:

> I mildly recalls seeing a bug like this. The problem was in intel's
> kernel driver. A NIC by defaul checks incoming packets whether they
> match NIC's MAC. So if a TAP device was created over a NIC, it had to be
> put into promisc mode (automatically done by the driver) to allow
> different MACs and the check was done in kernel then. But since this
> generates too much interrupts, NICs HW was extended and it can be
> programmed with multiple MACs to let through. However, there was a bug
> which I recall of, that intel driver was not always putting the TAP MAC
> into the NIC HW correctly. Obviously, the bug was not visible if the NIC
> was put into promisc mode. And this may be what you are seeing. Let me
> see if I can find the bug.

FYI - enabling promiscious mode on eth0 does not help. I have to enable
it on the macvtap0 which is on top of eth0.

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