-m mark --mark $from_untrusted/$MASK_FROM \
-m state --state ESTABLISHED
+m4_divert(60)m4_dnl
+###--------------------------------------------------------------------------
+### Kill things we don't understand properly.
+###
+### I don't like having to do this, but since I don't know how to do proper
+### multicast filtering, I'm just going to ban it from being forwarded.
+
+errorchain poorly-understood REJECT
+
+## Ban multicast destination addresses in forwarding.
+run iptables -A FORWARD -g poorly-understood \
+ -d 224.0.0.0/4
+run ip6tables -A FORWARD -g poorly-understood \
+ -d ff::/8
+
m4_divert(80)m4_dnl
###--------------------------------------------------------------------------
### Locally-bound packet inspection.