On Thu, 2015-04-09 at 10:47 +0200, Michal Privoznik wrote:

Ah, so that's not the bug then. Have you perhaps changed the vNIC MAC
inside the guest after it was started? Even though libvirt will nowadays
adapt to such change, older version of libvirt haven't this implemented
causing guest connectivity to break.

Nope. I only changed the nic mode from bridged to macvtap bridged mode but always followed by a shutdown / start of the VM.
Anyway it's only an ipv6 problem - i do not have this problem with ipv4!

Stefan