Mangling problem

["Regina Reine" <regina@erg.abdn.ac.uk>]

Hi,
I am doing an experiment with iptables. I use a hub to connect two
computers. Computer A captures the video packet (or any packets) and
computer B runs iptables and my code in Red Hat 8. Basically, with hub,
computer B will be able to see the packets coming to computer A. I would
like computer B to preroute this packet and put these packets in
userspace where I run my code. 

I uses :

** Iptables -t mangle -I PREROUTING -p udp -I eth0 -j QUEUE

However, seems like I only be able to capture broadcast packets. (But
TCPDUMP could see the udp packets). I have checked my code (just a
simple code that scan what kind of packets and it worked with udp
generator such as iperf or hping). 
I have tried a few other similar ways but still only could capture
broadcast packets. Does anybody spots my mistake or could give me advice
for better solution? Thank you

Best regards,
Regina Reine