====== Some theory ======
  * http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/antony/example.html

====== Praxis ======
  * Make sure that Multicast is enabled in kernel. May need recompiled.
  * ifconfig, check if interface has "MULTICAST".
  * ip route add 224.0.0.0/4 dev wlan0.
  * disable icmp_echo_ignore_broadcasts: echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts.