Subject: ip link macvtap interface not processing specific ipv6 multicast traffic without promiscuous mode on

From: Stefan Bauer <[email-masked]>
Date: Thu, 09 Apr 2015 12:09:27 +0200

Hi,

Linux s1 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt7-1 (2015-03-01) x86_64
GNU/Linux
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 10)

The following interface (created by kvm/qemu virtualization)

7: macvtap0@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc
pfifo_fast state UNKNOWN mode DEFAULT group default qlen 500
    link/ether 52:54:00:76:c1:f0 brd ff:ff:ff:ff:ff:ff

is not processing multicast traffic for ipv6 to specific addresses.
My virtual machines get router&prefix correct but can not resolve
addresses - hence are not able to communicate with other machines.

If i put the interface in promiscuous mode the neighbor tables of other
hosts are instantly filled. Without:
2a01:198:200:8350:98ec:1708:c82e:a4fb dev br-lan  INCOMPLETE With:
2a01:198:200:8350:98ec:1708:c82e:a4fb dev br-lan lladdr
52:54:00:8e:b9:eb REACHABLE

Any ideas on this?

Cheers,

Stefan