I have faced problems listening at sockets bound a multicast address. So, I decide to use your example application as model to test the multicast. This program is attached to this message. When I bind at multicast addresses 225.0.0.1, 226.0.0.1, …, 239.0.0.1, the tcp/ip stack don’t call the eth_ioctl routine, and didn’t register the address at the rash table. Consequently, the Net50 isn’t able to receive any packet at this address. I follow the setsockopt routine, and it call eth_ at arp_mult_add, after return from arp_mult_add. I wasn’t able to go futher, once I haven’t the sources. I am doing something wrong, I mean, doing a conceptual mistake? If not, someone could check this? Thansks,