Receiving the Multicast Listener Report

[Hitokage]

Hello.
I'd like to receive the multicast listener report that is sent as a reply to the Multicast listener query. My code however doesn't accept anything. I'd really appreciate any help.

Here is the wireshark screenshot. I am sending the query, getting the reply but cannot catch it with my program. At least one of them would be nice.

//...
//creating the socket
int ndpResFdLMNR = socket(AF_INET6, SOCK_RAW, IPPROTO_RAW);
	if (ndpResFdLMNR == -1)
	{
		std::cerr << "Cannot create the listening socket!";
		return FAIL_EXIT;
	}

//not sure if I have to do this but joining the ff02::c mcast group :-)
struct ipv6_mreq mreq;
mreq.ipv6mr_interface = if_nametoindex(interfaceName);
inet_pton(AF_INET6, "ff02::c",&(mreq.ipv6mr_multiaddr));	
setsockopt(ndpResFdLMNR, IPPROTO_RAW, IPV6_JOIN_GROUP, &mreq, sizeof(mreq)); //EDIT: I noticed that IPPROTO_RAW returns error here, changed to IPPROTO_IPV6 but still not working

//setting the timeout
setsockopt(ndpResFdLMNR, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));

//setting the reuse
int one = 1;
setsockopt(ndpResFdLMNR,SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));

//binding
struct sockaddr_in6 sa6LMNR;
sa6LMNR.sin6_family = AF_INET6;
sa6LMNR.sin6_port = 0;
sa6LMNR.sin6_flowinfo = 0;
sa6LMNR.sin6_scope_id = 0; //EDIT2: Also tried to put if_nametoindex(interfaceName) here
inet_pton(AF_INET6, "ff02::c",&(sa6LMNR.sin6_addr));
bind(ndpResFdLMNR, (struct sockaddr*)&sa6LMNR, sizeof(sa6LMNR));

	while (1)
	{		
		retVal6 = recvfrom(ndpResFdLMNR, &r, sizeof(lqPck), 0, (struct sockaddr*)&sourceRes, &len);
		if (retVal6 < 0)
			break;
		addIPv6(sourceRes);
	}

I am sorry if I'm missing something basic but I don't know where to look anymore . Have a nice day!

[VictorN]

inet_pton(AF_INET6, "ff02::c",&(mreq.ipv6mr_multiaddr));	
setsockopt(ndpResFdLMNR, IPPROTO_RAW, IPV6_JOIN_GROUP, &mreq, sizeof(mreq)); //EDIT: I noticed that IPPROTO_RAW returns error here, changed to IPPROTO_IPV6 but still not working

i

You have to check the exact error code/description to understans the reason of the problem.
And you should do it for every API/C-runtime function you are using.

[Hitokage]

You have to check the exact error code/description to understans the reason of the problem.
And you should do it for every API/C-runtime function you are using.

Thank you for the advice! I have tried to check every call there but no luck. It should work right now I think.

I am starting to think there is some flaw in my logic. Is it OK to join those specific multicast groups like ff02::c?

[VictorN]

I only can say you that this address looks like a valid one. You could check it in https://www.helpsystems.com/intermap...ess-validation
or some similar sites checking the IPv6 address validity.

[Hitokage]

Thanks for the effort. I'm still playing with the code but really no idea what's wrong here.

[VictorN]

What does the setsockopt return? If it is SOCKET_ERROR then why don't you call the WSAGetLastError to get the error status?

[Hitokage]

I am using Linux.

I did some edits to the code so it looks like this now:

        int ipv6RawFdRcv = socket(AF_INET6, SOCK_RAW, IPPROTO_IPV6);
        if (ipv6RawFdRcv == -1)
        {
                std::cerr << "Cannot create the IPV6 RAW listening socket!";
                return FAIL_EXIT;
        }
        int retVal = 0; 

        struct timeval timeout;
        timeout.tv_sec = 0;
        timeout.tv_usec = 20000;
        

        struct sockaddr_in6 sa6Lq;
        sa6Lq.sin6_family = AF_INET6;
        sa6Lq.sin6_port = 0;
        sa6Lq.sin6_scope_id = interfaceIndex;
        sa6Lq.sin6_addr = in6addr_any;
	struct ipv6_mreq mreq;
	mreq.ipv6mr_interface = interfaceIndex;

	struct sockaddr_in6 s;
        inet_pton(AF_INET6, "ff02::c",(&s.sin6_addr));       
	copyIpv6(s.sin6_addr.s6_addr, mreq.ipv6mr_multiaddr.s6_addr);	

	retVal = setsockopt(ipv6RawFdRcv, IPPROTO_IPV6, IPV6_JOIN_GROUP, &mreq, sizeof(mreq));
	std::cerr << retVal;

        retVal = setsockopt(ipv6RawFdRcv, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)); 
	std::cerr << retVal;

        int one = 1;
        retVal = setsockopt(ipv6RawFdRcv,SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
	std::cerr << retVal;

	retVal = bind(ipv6RawFdRcv, (struct sockaddr*)&sa6Lq, sizeof(sa6Lq));	
	std::cerr << retVal;

        len = sizeof(senderIp);
        bzero(&senderIp, sizeof(senderIp));
        struct lqPck r;
        while (1)
        {               
                retVal = recvfrom(ipv6RawFdRcv, &r, sizeof(lqPck), 0, (struct sockaddr*)&senderIp, &len);
                if (retVal < 0)
                        break;
                addIPv6(senderIp);

                std::cerr<< "Packet!"<< std::endl;
        }

What I get is: 0000

I am starting to think that the Linux kernel is filtering those packets preventing my application to get them

[VictorN]

I am using Linux.

I did some edits to the code so it looks like this now:

...

What I get is: 0000

I am starting to think that the Linux kernel is filtering those packets preventing my application to get them

Do you mean all of the socket functions you call here succeeded?

[Hitokage]

Do you mean all of the socket functions you call here succeeded?

It seems so.

[Hitokage]

So I have found a solution to my problem. Even though I still don't know why the code above doesn't work (as I said I suspect that those packets are somehow filtered since they are on a special purpose multicast addresses, I'd appreciate any explanation if somebody knows the reason though) I managed to catch them in a different way.

What I did is that I simply started accepting all packets and I am choosing the ones I need by checking the ethernet type value and then the IPV6 header info.
So basically using a socket like this:

socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))