ネットワークカード複数刺しで初回必ずタイムアウトする現象の対策方法

ありました。

    int port = 1234;

    IPHostEntry entry = Dns.GetHostEntry(Dns.GetHostName());

    //find ip address for your adapter here
    IPAddress localAddress = entry.AddressList.FirstOrDefault();

    IPEndPoint localEndPoint = new IPEndPoint(localAddress, port);

    //use socket instead of a TcpClient
    Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

    //binds client to the local end point
    client.Bind(localEndPoint);

http://stackoverflow.com/questions/49507/controlling-which-network-card-tcp-ip-message-are-sent-on