IGMP/Multicast routing in Linux

Disabling rp_filter fixed this problem.

echo "0" > /proc/sys/net/ipv4/conf/all/rp_filter

I've used tcpdunp a fair bit but don't find it very easy so I use ngrep which supports regex too.

ngrep -t -d eth3 '' broadcast and ngrep -t -d eth3 '' multicast should both put the interface into promiscuous mode and achieve the same thing.

I'm not suggesting that this is much different from what you're trying with tcpdump but in case for some reason it's misbehaving then ngrep is another tool on top of the Java tool to try.