I am new to FreeBSD so please forgive (and correct) wrong terminology and
concepts.
I’ve installed FreeBSD 11.2 as a VM host and run in to a problem with multicast
packets over a bridge not being seen by programs [on the host] listening on the
bridge’s physical interface constituent (igb1), which I discovered when running
avahi-daemon.
Briefly, my setup is as follows:
FreeBSD 11.2 host, bare metal, eth PHY igb1
bridge0 with members igb1, tap0, tap1
VM linux guest virtio-net to tap0 to bridge on FreeBSD
VM freebsd guest virtio-net to tap1 to bridge on FreeBSD
Mac, 802.11 to AP to same switch as FreeBSD
mDNS query/response operates properly between the mac and any of the others
(both physical and virtual), and all work in the converse direction with the
mac. The guests, all of which are constituents of the bridge, are able to
communicate via mDNS with one another. However, the guests are _unable_ to
communicate with the host via mDNS. tcpdump shows the query packets appearing
on igb1, but truss on avahi-daemon shows they are not received.
This means multicast packets are forwarded out all members of the bridge, but
not IN (at least, to physical interfaces — they do seem to go both directions
on the taps)
If I add an IP address to the bridge, avahi-daemon on the host binds to the
bridge interface directly and then receives incoming packets, responding with
the IP of the bridge. All then operates correctly, except that the host now has
two IPs on the same subnet of course.
My question is: given that if_bridge(4) is described as a virtual switch:
A bridge works like a switch, forwarding traffic from one interface to
another. Multicast and broadcast packets are always forwarded to all
interfaces that are part of the bridge. For unicast traffic, the bridge
learns which MAC addresses are associated with which interfaces and will
forward the traffic selectively.
and given that unicast packets originating on one of the bridge’s taps are
received by host programs bound to igb1, it seems to me that anything bound to
igb1 should also be receiving the multicast packets.
Is this an error specifically related to multicast and bridging, or is it an
accident that unicast connections work? (or, none of the above)
Kind regards and thanks in advance.
jsb
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