[Bug 234472] CARP using wrong multicast MAC destination (was: Missing outgoing CARP traffic on interface)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=234472

--- Comment #10 from Andreas Pflug <pgadmin at pse-consulting.de> ---
AFAICS the rule actually does as advised, since naively speaking 224.0.0.18
isn't in the ix4 network and so anything should be routed to the stdgw.
But it's IP multicast, and so route-to shouldn't be applied in any case on
224.0.0.0/4, according to RFC1112.

I added "pass out quick from {ix4} to 224.0.0.0/4" before that route-to rule,
preventing the misshaped multicast packet.

So actually pf does as advised to straight forward, but this will break
multicast specifications. IMHO pf should implement the special behaviour on
multicast packets implicitely, i.e. excepting them from routing, because this
issue has been around for years without being diagnosed correctly (probably
blaming some innocent switch IGMP implementations), and users probably don't
expect a standard default gateway routing command breaking local multicast
traffic.

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