This affects Linux 2.2 and 2.4 Using libpcap to put the interface in promiscuous mode, will cause that ifconfig(8) doesn't show it! libpcap uses setsockopt(..., SOL_PACKET, PACKET_ADD_MEMBERSHIP, ...) with PACKET_MR_PROMISC to set the interface in promiscuous mode. I notified this to the tcpdump-workers mailing list and the problem is that the setsockopt() sets the promisc flag in a variable that is not the same as the one that the SIOCGIFFLAGS ioctl() reads. I don't have the kernel source right now to make this advisory more precise. Well, sorry for my not-so-good english Enjoy
