## of weird stuff happens on lo, and it's best not to second-guess it.
run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
-## Local bootp packets have bizarre addresses. Don't block them just because
-## of this.
+## Local broadcast and link-local multicast packets sometimes have bizarre
+## addresses. Don't block them just because of this.
run iptables -t mangle -A in-classify -j RETURN \
-s 0.0.0.0 -d 255.255.255.255 \
- -p udp --source-port $port_bootpc --destination-port $port_bootps
+ -p udp
+run iptables -t mangle -A in-classify -j RETURN \
+ -s 0.0.0.0 -d 224.0.0.0/24 \
+ -p udp
## Since packets with source and destination addresses both local will go
## over the loopback interface, I shouldn't see a packet from me over any
## other interface. Except that I will if I sent a broadcast or multicast.
-## Allow the broadcasts, and remember not to trust them.
+## Allow the broadcasts, and remember not to trust them. There are no
+## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
+## to worry about that.
run iptables -t mangle -A local-source -j RETURN \
-m addrtype --dst-type BROADCAST
run iptables -t mangle -A local-source -j RETURN \
-s $addr
done
+## It's not valid to have a multicast address as a packet source: multicast
+## routing is done away from the source, so a multicast address would make
+## this impossible to do. So discard these packets. Also discard class-E
+## IPv4 addresses, since they aren't assigned.
+run iptables -t mangle -A in-classify -g bad-source-address \
+ -s 224.0.0.0/3
+run ip6tables -t mangle -A in-classify -g bad-source-address \
+ -s ff00::/8
+
m4_divert(41)m4_dnl
## Define the important networks.
for pass in 1 2; do