Hello Everyone,
I am currently using macOS 15.5 and XCode 16.4.
I am using the following code to send/receive multicast packets on multicast group ff02::1 and port 49153 using Apple NF's NWConnectionGroup.
import Network
import Foundation
// Creating a mutlicast group endpoint
let multicastIPv6GroupEndpoint: NWEndpoint = NWEndpoint.hostPort(host: NWEndpoint.Host.ipv6(IPv6Address("ff02::1")!), port: NWEndpoint.Port("49153")!)
do {
let multicastGroupDescriptor: NWMulticastGroup = try NWMulticastGroup (for: [multicastIPv6GroupEndpoint])
let multicastConnectionGroupDescriptor = NWConnectionGroup (with: multicastGroupDescriptor, using: .udp)
multicastConnectionGroupDescriptor.stateUpdateHandler = { state in
print ("🕰️ Connection Group state: \(state)")
if state == .ready {
multicastConnectionGroupDescriptor.send (content: "👋🏻 Hello from the Mac 💻".data (using: .utf8)) { err in
print ("➡️ Now, I am trying to send some messages.")
if let err = err {
print ("💥 Error sending multicast message: \(err)")
} else {
print ("🌚 Initial multicast message sent")
}
}
}
}
multicastConnectionGroupDescriptor.setReceiveHandler { message, content, isComplete in
if let content = content, let messageString = String (data: content, encoding: .utf8) {
print ("⬅️ Received message: \(messageString)")
}
}
multicastConnectionGroupDescriptor.start (queue: .global())
} catch {
print ("💥 Error while creating Multicast Group: \(error)")
}
RunLoop.main.run()
I am able to successfully create a NWConnectionGroup without any warnings/errors.
The issue occurs when the stateUpdateHandler's callback gets invoked.
It first gives me this warning:
nw_listener_socket_inbox_create_socket IPV6_LEAVE_GROUP ff02::1.49153 failed [49: Can't assign requested address
But then it shows me that the state is ready:
🕰️ Connection Group state: ready
After this, when the send is performed, it gives me a bunch of errros:
nw_endpoint_flow_failed_with_error [C1 ff02::1.49153 waiting parent-flow (unsatisfied (Local network prohibited), interface: en0[802.11], ipv4, ipv6, uses wifi)] already failing, returning
nw_socket_connect [C1:1] connectx(7, [srcif=0, srcaddr=::.62838, dstaddr=ff02::1.49153], SAE_ASSOCID_ANY, 0, NULL, 0, NULL, SAE_CONNID_ANY) failed: [48: Address already in use]
nw_socket_connect [C1:1] connectx failed (fd 7) [48: Address already in use]
nw_socket_connect connectx failed [48: Address already in use]
nw_endpoint_flow_failed_with_error [C1 ff02::1.49153 in_progress socket-flow (satisfied (Path is satisfied), interface: en0[802.11], ipv4, ipv6, dns, uses wifi)] already failing, returning
There is no other background process running on the same port. I tried using different ports as well as multicast groups but the same error persists.
The same code works fine for an IPv4 multicast group.
I have following questions:
Why am I getting these errors specifically for IPv6 multicast group but not for IPv4 multicast group?
Are there any configurations that needed to be done in order to get this working?
