I wrote a small Swift program that should send a Hello World! UDP package to any IPv6 link-local node that’s listening. However, using netcat via nc -l 1234 to listen for the message on port 1234 never receives it. Here’s my code (this class instance is being kept alive inside a SwiftUI view):

@Observable
class NetworkService {
    let conn: NWConnection
    let monitor: NWPathMonitor
    
    init() {
        monitor = NWPathMonitor()
        conn = NWConnection(host: .ipv6(IPv6Address("ff02::1%lo0")!), port: 1234, using: .udp)
        start()
    }
    
    
    func start() {
        conn.send(content: "Hello from Swift!".data(using: .utf8), completion: .idempotent)

        conn.start(queue: .main)
        
        print("Done!")
    }
    
    
}

I’ve tried to send a UDP package to the multicast IPv6 address of link-local nodes, on interface lo0 and expected necat client to receive it.