INADDR_ALLRTRS_GROUP
mcast_addr.imr_multiaddr.s_addr = htonl(INADDR_ALLRTRS_GROUP);
sadest.sin_addr.s_addr = htonl(INADDR_ALLRTRS_GROUP);
#ifndef INADDR_ALLRTRS_GROUP
allrtrs_group = htonl(INADDR_ALLRTRS_GROUP);