IPv4 Multicast MAC Address issues

[Peter Jeremy]

I'm trying to use multicast on my home network for the first time and
have found an apparent anomoly in the destination MAC address.

My reading of RFC1112 section 6.4 is that the the destination MAC
address uses the low 23 bits of the destination (multicast) IP
address.  This is what Linux and Windows do and ifmcstat(8) on
FreeBSD shows that as the multicast MAC filter.  Unfortunately, it
seems that (at least on FreeBSD-10), the destination MAC address
uses the low 23 bits of the IP address of my default route.

I am not doing any special multicast-related configuration on any
of the hosts and have been using ping(8) to generate multicast
packets.

Does FreeBSD need special configuration to support multicast or is this
a bug?

-- 
Peter Jeremy
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