Specify what interface use to send multicast IGMP JOIN (c# socket)

Question

I would like to choose which network interface to use to send a join request. This is the code I tried but I don't think it's right:

static int GetNicIndexByIP(String ipAddress)
{
    int adapterIndex = -1;
    IPAddressInformation[] adapterIPs;

    foreach (NetworkInterface adapter in nics)
    {
        adapterIPs = adapter.GetIPProperties().UnicastAddresses.ToArray();
        adapterIndex = (int)IPAddress.HostToNetworkOrder(adapter.GetIPProperties().GetIPv4Properties().Index);

        foreach (IPAddressInformation ip in adapterIPs)
        {
            if (ip.Address.ToString() == ipAddress)
                return adapterIndex;
        }
    }

    return -1;
}


string nicAddress = "192.168.1.100";
string multicastAddress = "229.1.0.1";
int nicIndex = GetNicIndexByIP(nicAddress);
Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

// first try: ignored (sent from another interface)
client.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastInterface, nicIndex);
client.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(IPAddress.Parse(multicastAddress)));

// second try: error argument "229.1.0.1" out of range
client.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(IPAddress.Parse(multicastAddress), nicIndex));

So, you would like to detect the network interface with multicast address? — Pavel Anikhouski
– Pavel Anikhouski, Commented Jun 1, 2020 at 7:33
I would like to send the join packet from a specific interface — Rick
– Rick, Commented Jun 1, 2020 at 7:47

Rick · Accepted Answer · 2020-06-01 12:29:51Z

0

if anyone is interested, I found the answer myself:

MulticastOption mcastOption = new MulticastOption(IPAddress.Parse(multicastAddress), IPAddress.Parse(nicAddress));
client.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, mcastOption);

answered Jun 1, 2020 at 12:29

Rick

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