I have written an ipv6 multicast program on windows xp sp3. But a problem bothers me a lot. The sendto function implies no error, but I can't capture the packet using wireshark. I am sure the filter is right. Thanks in advance. And the code is as follows: #include "stdafx.h" #include <stdio.h> /* for printf() and fprintf() */ #include <winsock2.h> /* for socket(), connect(), sendto(), and recvfrom() */ #include <ws2tcpip.h> /* for ip_mreq */ #include <stdlib.h> /* for atoi() and exit() */ #include <string.h> /* for memset() */ #include <time.h> /* for timestamps */ #include <pcap.h> #include <Iphlpapi.h> #pragma comment(lib, "Ws2_32.lib") #pragma comment(lib, "wpcap.lib") #pragma comment(lib, "Iphlpapi.lib") int _tmain(int argc, _TCHAR* argv[]) { int sfd; int on, length, iResult; WSADATA wsaData; struct addrinfo Hints; struct addrinfo *multicastAddr, *localAddr; char buf[46]; // Initialize Winsock iResult = WSAStartup(MAKEWORD(2, 2), &wsaData); if (iResult != 0) { printf("WSAStartup failed: %d\n", iResult); return 1; } /* Resolve destination address for multicast datagrams */ memset(&Hints, 0, sizeof (Hints)); Hints.ai_family = AF_INET6; Hints.ai_socktype = SOCK_DGRAM; Hints.ai_protocol = IPPROTO_UDP; Hints.ai_flags = AI_NUMERICHOST; iResult = getaddrinfo("FF02::1:2", "547", &Hints, &multicastAddr); if (iResult != 0) { /* error handling */ printf("socket error: %d\n", WSAGetLastError()); return -1; } /* Get a local address with the same family (IPv4 or IPv6) as our multicast group */ Hints.ai_family = multicastAddr->ai_family; Hints.ai_socktype = SOCK_DGRAM; Hints.ai_flags = AI_PASSIVE; /* Return an address we can bind to */ if ( getaddrinfo(NULL, "546", &Hints, &localAddr) != 0 ) { printf("getaddrinfo() failed: %d\n", WSAGetLastError()); exit(-1); } // Create sending socket //sfd = socket (multicastAddr->ai_family, multicastAddr->ai_socktype, multicastAddr->ai_protocol); sfd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); if (sfd == -1) { printf("socket error: %d\n", WSAGetLastError()); return 0; } /* Bind to the multicast port */ if ( bind(sfd, localAddr->ai_addr, localAddr->ai_addrlen) != 0 ) { printf("bind() failed: %d\n", WSAGetLastError()); exit(-1); } if (multicastAddr->ai_family == AF_INET6 && multicastAddr->ai_addrlen == sizeof(struct sockaddr_in6)) /* IPv6 */ { on = 1; if (setsockopt (sfd, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char *)&on, sizeof (on) /*(char *)&interface_addr, sizeof(interface_addr)*/) == -1) { printf("setsockopt error:%d\n", WSAGetLastError()); return -1; } if (setsockopt (sfd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, (char *)&on, sizeof (on) /*(char *)&interface_addr, sizeof(interface_addr)*/) == -1) { printf("setsockopt error:%d\n", WSAGetLastError()); return -1; } struct ipv6_mreq multicastRequest; /* Multicast address join structure */ /* Specify the multicast group */ memcpy(&multicastRequest.ipv6mr_multiaddr, &((struct sockaddr_in6*)(multicastAddr->ai_addr))->sin6_addr, sizeof(struct in6_addr)); /* Accept multicast from any interface */ multicastRequest.ipv6mr_interface = 0; /* Join the multicast address */ if ( setsockopt(sfd, IPPROTO_IPV6, IPV6_JOIN_GROUP, (char*) &multicastRequest, sizeof(multicastRequest)) != 0 ) { printf("setsockopt() failed: %d\n", WSAGetLastError()); return -1; } on = 1; if (setsockopt (sfd, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char *)&on, sizeof (on)) == -1) { printf("setsockopt error:%d\n", WSAGetLastError()); return 0; } } memset(buf, 0, sizeof(buf)); strcpy(buf, "hello world"); iResult = sendto(sfd, buf, strlen(buf), 0, (LPSOCKADDR) multicastAddr->ai_addr, multicastAddr->ai_addrlen); if (iResult == SOCKET_ERROR) { printf("setsockopt error:%d\n", WSAGetLastError()); return -1; /* Error handling */ } return 0; }