Hi! I am using BSD sockets in Ubuntu 9.10 to send UDP packets in broadcast with the following code: sock_fd = socket(PF_INET,SOCK_DGRAM,IPPROTO_UDP); //sock_fd=socket(AF_INET,SOCK_DGRAM,0); receiver_addr.sin_family = PF_INET; //does not send with broadcast in ad hoc receiver_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST); inet_aton("169.254.255.255",&receiver_addr.sin_addr); receiver_addr.sin_port = htons(port); int broadcast = 1; // this call is what allows broadcast packets to be sent: if (setsockopt(sock_fd, SOL_SOCKET, SO_BROADCAST, &broadcast, sizeof broadcast) == -1) { perror("setsockopt (SO_BROADCAST)"); exit(1); } ret=sendto(sock_fd, packet, size, 0,(struct sockaddr*)&receiver_addr,sizeof(receiver_addr)); Note that is not all the code, it is only to have an idea. The program sends all the data with INADDR_BROADCAST if I am connected to an infrastructure wireless network. However, if my laptop is connected to an ad-hoc network, it is able to receive all the data, but not to send it. I have solved the problem using the 169.254.255.255 broadcast address, but I would like to know what is going on. Thank you in advance!