如何接收多播加入报告 (IGMP v3)

Question

I want to see which Multicast-Join-Reports fly through the.network in which my host computer resides in. For that I've written a little TypeScript program, that joins the multicast group '224.0.0.22', which is defined in RFC3376 under 4.2.14 as the IP Destination for Multicast-Join-Reports. But I receive no requests even when I should, because I'am watching traffic via Wireshark and there Multicast-Join-Reports are send and received.

Edit 1 : Attached is the receiving part:

const interfaces = os.networkInterfaces();

const IGMP_V3_REPORT_MULTICAST_ADDRESS = '224.0.0.22';
const socket = dgram.createSocket('udp4');

const ipv4Interface = interfaces['eth0'].find((i) => i.family === 'IPv4');

if (ipv4Interface) {
    socket.on('error', (e: Error) => {
        console.log(`${ifaceName}: socket error: ${e}`);
        sockResults[index] = false;
    });

    socket.on('listening', () => {
        const address = socket.address();
        console.log(`${ifaceName}: listening on ${address.address}:${address.port}`);

        console.log(`${ifaceName}: joining multicast group with address: ${IGMP_V3_REPORT_MULTICAST_ADDRESS} for local address: ${ipv4Interface.address}`);
        socket.addMembership(IGMP_V3_REPORT_MULTICAST_ADDRESS, ipv4Interface.address);
    })

    socket.on('message', (msg, rinfo) => {
        console.log(`${ifaceName}: got ${msg}`);
    });

    socket.bind(0);

    setTimeout(() => {
        console.log(`${ifaceName}: dropping multicast membership for ${IGMP_V3_REPORT_MULTICAST_ADDRESS}`);
        socket.dropMembership(IGMP_V3_REPORT_MULTICAST_ADDRESS,  ipv4Interface.address);

        console.log(`${ifaceName}: closing socket`);
        socket.close();

        resolve();
    }, 120 * 1000);
}

Answer 1

Let's ignore IGMP, multicast-join, switches, and all that stuff for a moment, as you're already physically receiving the desired packets.

If you want to receive packets that are destined to 239.255.255.250 , you're gonna have to use that address (and for UPnP the relevant port) in socket.bind() .

These are all Python implementations, but hopefully converting to TypeScript won't be difficult: https://github.com/leslie-wang/py-multicast-example/blob/master/mcast.py and this .

Specifically, you need to:

socket.bind((MCAST_GRP, MCAST_PORT))

which in your case should be ('239.255.255.250', 1900) , which are the default for UPnP.

Whereas, you are binding to "any available port" with socket.bind(0) .

And I believe the parameters given to socket.addMembership() , should be the mcast group you want to receive messages from. The kernel, specifically the code that handles IP, needs to know to "forward" these packets upwards towards UDP.

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By the way... there's also the option of sniffing instead of listening, in your use-case, but it may require higher privileges.