using System.Net;
using System.Net.Sockets;

public static class GetAvailablePort 
{

public static int GetAvailableUdpPort()
{
    using var socket = new Socket(
        AddressFamily.InterNetwork,
        SocketType.Dgram,
        ProtocolType.Udp
    );

    socket.Bind(new IPEndPoint(IPAddress.Any, 0));

    return ((IPEndPoint)socket.LocalEndPoint).Port;
}
}