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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
* Service stub name, use interface name + Local if not set
     */
    String stub() default "";
    /**
     * Cluster strategy, legal values include: failover, failfast, failsafe, failback, forking
     * you can use {@link org.apache.dubbo.common.constants.ClusterRules#FAIL_FAST} ……
     */
    String cluster() default ClusterRules.EMPTY;
    /**
     * Maximum connections service provider can accept, default value is 0 - connection is shared
     */
    int connections() default -1;
    /**
     * The callback instance limit peer connection
     * <p>
     * see org.apache.dubbo.rpc.Constants#DEFAULT_CALLBACK_INSTANCES
     */
    int callbacks() default -1;
    /**
     * Callback method name when connected, default value is empty string
     */
    String onconnect() default "";
    /**
     * Callback method name when disconnected, default value is empty string
     */
    String ondisconnect() default "";
    /**
     * Service owner, default value is empty string
     */
    String owner() default "";