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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 layer, default value is empty string
     */
    String layer() default "";
    /**
     * Service invocation retry times
     * <p>
     * see Constants#DEFAULT_RETRIES
     */
    int retries() default -1;
    /**
     * Load balance strategy, legal values include: random, roundrobin, leastactive
     * you can use {@link org.apache.dubbo.common.constants.LoadbalanceRules#RANDOM} ……
     */
    String loadbalance() default LoadbalanceRules.EMPTY;
    /**
     * Whether to enable async invocation, default value is false
     */
    boolean async() default false;
    /**
     * Maximum active requests allowed, default value is 0
     */
    int actives() default -1;
    /**
     * Whether the async request has already been sent, the default value is false
     */
    boolean sent() default false;
    /**
     * Service mock name, use interface name + Mock if not set
     */