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操作步骤如下：
1. k8s环境下，consumer端开启mesh模式
2. consumer端需要调用多个provider
3. provider有应用级注册和接口级注册，并且需要的provider不再同一个namespace下
4. 原有项目存在dubbo2.6与3.1多版本间的相互调用，在开启消费端mesh（dubbo3.1）后，无法调用到2.6的服务提供者

**问题：**

1. 如何实现在一个consumer下，调用多个namespace下的provider，并且provider有应用级注册和接口级注册
2. dubbo3.1消费端在开启mesh后，如何调用版本是2.6的服务提供者
* Actually，when the {@link ExtensionLoader} init the {@link Protocol} instants,it will automatically wrap three
     * layers, and eventually will get a <b>ProtocolSerializationWrapper</b> or <b>ProtocolFilterWrapper</b> or <b>ProtocolListenerWrapper</b>
     */
    private Protocol protocolSPI;
    /**
     * A {@link ProxyFactory} implementation that will generate a reference service's proxy,the JavassistProxyFactory is
     * its default implementation
     */
    private ProxyFactory proxyFactory;
    private ConsumerModel consumerModel;
    /**
     * The interface proxy reference
     */
    private transient volatile T ref;
    /**
     * The invoker of the reference service
     */
    private transient volatile Invoker<?> invoker;
    /**
     * The flag whether the ReferenceConfig has been initialized
     */
    private transient volatile boolean initialized;
    /**
     * whether this ReferenceConfig has been destroyed
     */
    private transient volatile boolean destroyed;
    /**
     * The service names that the Dubbo interface subscribed.
     *
     * @since 2.7.8