Receiving the Multicast Listener Report

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.

Code:

---

//...
//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 :D. Have a nice day!

Quote:

---

Code:

---

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.

Quote:

---

Originally Posted by VictorN

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?

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.

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

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

I am using Linux.

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

Code:

---

        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 :D

Quote:

---

Originally Posted by Hitokage

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 :D

---

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

Quote:

---

Originally Posted by VictorN

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

---

It seems so.

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:

Code:

---

socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))

---