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IPv6 Multicast not working

Beosar · 2018-04-25T16:21:35

Hi, I tried to send an ipv6 multicast packet through my network. The sending seems to work, since it arrives on the destination PC - at least it appears in the logged network traffic in WireShark. But it does not arrive in my server program. When I send a packet from the same PC that should receive it, it does work though. This is the code for sending: UDPBroadcastSocket = socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP); BOOL Yes = 1; setsockopt(UDPBroadcastSocket, IPPROTO_IPV6, IPV6_V6ONLY, (char*)&Yes, sizeof(BOOL)); int32_t hops = 50; setsockopt(UDPBroadcastSocket, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, (char*)&hops, sizeof(hops)); uint32_t IF = 0; setsockopt(UDPBroadcastSocket, IPPROTO_IPV6, IPV6_MULTICAST_IF, (char*)&IF, sizeof(IF)); struct sockaddr_in6 sock_in; struct addrinfo *result = NULL; struct addrinfo hints; 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; getaddrinfo("FF18::1243", "12346", &hints, &result); unsigned char buffer[MAXBUF]; int PacketSize = 8; int sinlen = int(result->ai_addrlen); memcpy(&sock_in, result->ai_addr, result->ai_addrlen); freeaddrinfo(result); sendto(UDPBroadcastSocket, (char*)buffer, PacketSize, 0, (sockaddr *)&sock_in, sinlen); And this is the code for receiving the packet: std::vector<uint32_t> GetNetworkInterfaceIndices(){ std::vector<uint32_t> Result = { 0 }; /* Declare and initialize variables */ DWORD dwSize = 0; DWORD dwRetVal = 0; unsigned int i = 0; // Set the flags to pass to GetAdaptersAddresses ULONG flags = GAA_FLAG_INCLUDE_PREFIX; // default to unspecified address family (both) ULONG family = AF_UNSPEC; LPVOID lpMsgBuf = NULL; PIP_ADAPTER_ADDRESSES pAddresses = NULL; ULONG outBufLen = 0; ULONG Iterations = 0; PIP_ADAPTER_ADDRESSES pCurrAddresses = NULL; PIP_ADAPTER_UNICAST_ADDRESS pUnicast = NULL; PIP_ADAPTER_ANYCAST_ADDRESS pAnycast = NULL; PIP_ADAPTER_MULTICAST_ADDRESS pMulticast = NULL; IP_ADAPTER_DNS_SERVER_ADDRESS *pDnServer = NULL; IP_ADAPTER_PREFIX *pPrefix = NULL; family = AF_INET6; // Allocate a 15 KB buffer to start with. outBufLen = WORKING_BUFFER_SIZE; do { pAddresses = (IP_ADAPTER_ADDRESSES *)MALLOC(outBufLen); if (pAddresses == NULL) { return{ 0 }; } dwRetVal = GetAdaptersAddresses(family, flags, NULL, pAddresses, &outBufLen); if (dwRetVal == ERROR_BUFFER_OVERFLOW) { FREE(pAddresses); pAddresses = NULL; } else { break; } Iterations++; } while ((dwRetVal == ERROR_BUFFER_OVERFLOW) && (Iterations < MAX_TRIES)); if (dwRetVal == NO_ERROR) { // If successful, output some information from the data we received pCurrAddresses = pAddresses; while (pCurrAddresses) { Result.emplace_back(pCurrAddresses->IfIndex); pCurrAddresses = pCurrAddresses->Next; } } else { return{ 0 }; } if (pAddresses) { FREE(pAddresses); } return Result; } UDPSocket = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); sockaddr_in6 UDP_Sock_in; memset(&UDP_Sock_in, 0, sizeof(sockaddr_in6)); UDP_Sock_in.sin6_addr = in6addr_any; UDP_Sock_in.sin6_port = htons(Settings::GetPort()+1); UDP_Sock_in.sin6_family = PF_INET6; setsockopt(UDPSocket, IPPROTO_IPV6, IPV6_V6ONLY, (char*)&No, sizeof(BOOL)); bind(UDPSocket, (sockaddr*)&UDP_Sock_in, sizeof(UDP_Sock_in)); ipv6_mreq BroadcastGroup; memset(&BroadcastGroup, 0, sizeof(ipv6_mreq)); const auto IfIndices = GetNetworkInterfaceIndices(); BroadcastGroup.ipv6mr_multiaddr.u.Byte[0] = 0xFF; BroadcastGroup.ipv6mr_multiaddr.u.Byte[1] = 0x18; BroadcastGroup.ipv6mr_multiaddr.u.Byte[14] = 0x12; BroadcastGroup.ipv6mr_multiaddr.u.Byte[15] = 0x43; for (const auto& Index : IfIndices) { BroadcastGroup.ipv6mr_interface = Index; setsockopt(UDPSocket, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, (char*)&BroadcastGroup, sizeof(ipv6_mreq)); } socklen_t fromLength = sizeof(sockaddr_in6); pollfd PollFd; PollFd.events = POLLIN; PollFd.fd = UDPSocket; PollFd.revents = -1; WSAPoll(&PollFd, 1, -1); recvfrom(UDPSocket, (char*)buffer, MAXBUF, 0, (sockaddr*)&from, &fromLength); I basically tried specifying every single network interface index and the packet still does not arrive in the server. I have no idea what could be wrong. And why does it work when sender and receiver are on the same PC? I don't understand this. Does anyone have an idea? I'm trying this for like 5 hours now and I'm frustrated.

Networking and Multiplayer Programming

Started by Beosar April 21, 2018 12:41 AM

12 comments, last by hplus0603 6 years, 2 months ago

DexterZ101

301

April 25, 2018 12:18 PM

I haven't seen a computer station with a protocol that only uses IPV6, sometime IPV4 only but the default windows setting is IPV6 and IPV4 enabled on most devices, Multicast using IPV4 is the best option when announcing your game across local sub-net.

Just don't broadcast your created game 60 times a second : - D to not disrupt and flood other connected devices within the sub-net
and stop broadcasting if a certain condition is met E.g: if all players are connected, your last broadcast maybe saying the game is FULL or STARTED.

I broadcast my game every 256ms which 4 times a second and it is still seamless ^_^y

swiftcoder

18,997

April 25, 2018 02:00 PM

1 hour ago, DexterZ101 said:

Just don't broadcast your created game 60 times a second : - D to not disrupt and flood other connected devices within the sub-net

This is an area where mDNS shines. Rather than continuously broadcast from just the server, it broadcasts only changes in state (either a new service being advertised, or a new client connecting to the network). This allows building exponential backoff into all clients, which means that it's only chatty immediately after a state change, and quickly settles back down.

4 times a second seems very aggressive for a continuous broadcast.

Tristam MacDonald. Ex-BigTech Software Engineer. Future farmer. [https://trist.am]

hplus0603

11,919

April 25, 2018 04:21 PM

Yeah, 4 times a second seems high :-)

Another option to reduce broadcast is for the client to broadcast a "solicit" that servers answer to, rather than the server blindly broadcasting. Clients can also look for other clients soliciting, if servers also answer using broadcast, and hold off on soliciting themselves if they've seen a request in the last (500 + random(0, 1000)) milliseconds. This can be effectively instant when the client joins, because it can send its first solicit right away, and usually, active servers will immediately answer.

mDNS is pretty good. If you want a drop-in solution that works, use that. Only go to your own broadcast if you find that you need faster response, or for some other reason need custom functionality.

enum Bool { True, False, FileNotFound };