Question: UDP multicast on IPv6

[svdo]

Hi,

I've been struggling with an issue for days now, without any success. The platform on which I'm trying to do this is iOS (using Swift). I have a GCDAsyncUdpSocket and configure it like this:

self.socket!.setIPv4Enabled(false)
self.socket!.setIPv6Enabled(true)
do {
    try self.socket!.bindToPort(Announcement.ipv6BroadcastPort, interface: "en0")
}
catch let error {
    print("bind failed: \(error)")
    throw error
}
do {
    try self.socket!.joinMulticastGroup("ff32::5222", onInterface: "en0")
}
catch let e {
    print("join multicast failed: \(e)")
}

This calls both succeed. I verified that by stepping through the GCDAsyncUDPSocket code. After that, I try to send some data to a multicast address:

socket.sendData(data, toHost:"ff32::5222", port: 21026, withTimeout: 5, tag: 0)

At that point, when stepping through the GCDAsyncUDPSocket code, I end up in a call to sendto in the method doSend (line 3919). This call returns -1 and the error is "no route to host". I'm running this in the iOS simulator. Just to provide a bit more detail: when I enumerate all available network interfaces, I get this:

Name: lo0
Address: Optional("::1e89:f019:100:0")
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: lo0
Address: Optional("127.0.0.1")
Family: NetUtils.Interface.Family.ipv4
Supports multicast: true

Name: lo0
Address: nil
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: en0
Address: nil
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: en0
Address: Optional("10.0.42.20")
Family: NetUtils.Interface.Family.ipv4
Supports multicast: true

Name: en0
Address: Optional("2001:984:3427:1:1e89:f019:100::")
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: en0
Address: Optional("2001:984:3427:1:1e89:f019:100::")
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: en0
Address: Optional("4011:4fae:a00:2a24:1e89:f019:100::")
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: awdl0
Address: nil
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: utun0
Address: nil
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Name: utun0
Address: Optional("fde6:4b33:67e4:9d5e:1e89:f019:100::")
Family: NetUtils.Interface.Family.ipv6
Supports multicast: true

Any help is much appreciated!

[ghost]

Please take a look at #239 and https://groups.google.com/forum/#!topic/cocoaasyncsocket/Z9lqXGpR-kU.

[svdo]

Thanks @MeckiCologne. I have solved my issue, I succeeded in doing a send/receive over IPv6 UDP Multicast. The problem turned out to be a combination of issues. The posts that you mentioned were definitely relevant, I had also found them earlier and indeed setting the socket option IPV6_MULTICAST_IF turned out to be necessary for the sending to work. (Receiving doesn't seem to require it.) I'm still working on cleaning things up and moving my proof of concept towards the code that I really want to have, but people interested can look here: https://source.ind.ie/project/pulse-swift/blob/28bd0f48e3d4fa99f6095321a89036863c3f7a83/pulse-swift/discovery/Greeter.swift.