Listing 3. iptables Commands to Route UDP Packets on Port 1331 to
NFQUEUE

// Set up a new chain in the mangle table.
 iptables -t mangle -N PktMangle
// In the mangle FORWARD chain, route UDP packets
// to the new chain.
 iptables -t mangle -A FORWARD -p udp -m udp \
    --dport 1331 -j PktMangle
// Log the packet and invoke the queue facility.
 iptables -t mangle -A PktMangle -j LOG \
    --log-level info  --log-prefix "PktMangle rule"
 iptables -t mangle -A PktMangle -j QUEUE