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

[Stefan Bauer]

I could narrow down the problem. Win7Prof and Windows 10 is having this
issue.

Win Client is member of the multicast group and is listening on
ff02::1:ffdf:fe88

Traffic from router -> client - captured on router:

07:41:23.104567 IP6 fe80::12fe:edff:fee6:cfa > ff02::1:ffdf:fe88: ICMP6,
neighbor solicitation, who has 2a01:198:200:8350:851e:21a7:28df:fe88,
length 32
07:41:24.099764 IP6 fe80::12fe:edff:fee6:cfa > ff02::1:ffdf:fe88: ICMP6,
neighbor solicitation, who has 2a01:198:200:8350:851e:21a7:28df:fe88,
length 32
07:41:25.099772 IP6 fe80::12fe:edff:fee6:cfa > ff02::1:ffdf:fe88: ICMP6,
neighbor solicitation, who has 2a01:198:200:8350:851e:21a7:28df:fe88,
length 32


Traffic from router to client - captured on KVM HOST

09:41:23.106444 IP6 fe80::12fe:edff:fee6:cfa > ff02::1:ffdf:fe88: ICMP6,
neighbor solicitation, who has 2a01:198:200:8350:851e:21a7:28df:fe88,
length 32
09:41:24.101647 IP6 fe80::12fe:edff:fee6:cfa > ff02::1:ffdf:fe88: ICMP6,
neighbor solicitation, who has 2a01:198:200:8350:851e:21a7:28df:fe88,
length 32
09:41:25.101718 IP6 fe80::12fe:edff:fee6:cfa > ff02::1:ffdf:fe88: ICMP6,
neighbor solicitation, who has 2a01:198:200:8350:851e:21a7:28df:fe88,
length 32

No traffic seen on KVM GUEST (win7 or win10) with wireshark

Any ideas to debug this further?

Cheers

Stefan