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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
String REGISTRY_KEY = "registry";
    String REGISTRY_CLUSTER_KEY = "REGISTRY_CLUSTER";
    String REGISTRY_CLUSTER_TYPE_KEY = "registry-cluster-type";
    String REGISTRY_PROTOCOL = "registry";
    String DYNAMIC_KEY = "dynamic";
    String CATEGORY_KEY = "category";
    String PROVIDERS_CATEGORY = "providers";
    String CONSUMERS_CATEGORY = "consumers";
    String ROUTERS_CATEGORY = "routers";
    String DYNAMIC_ROUTERS_CATEGORY = "dynamicrouters";
    String DEFAULT_CATEGORY = PROVIDERS_CATEGORY;
    String CONFIGURATORS_CATEGORY = "configurators";
    String ALL_CATEGORIES = "providers,configurators,routers";
    String DYNAMIC_CONFIGURATORS_CATEGORY = "dynamicconfigurators";
    String APP_DYNAMIC_CONFIGURATORS_CATEGORY = "appdynamicconfigurators";
    String ROUTERS_SUFFIX = ".routers";
    String EMPTY_PROTOCOL = "empty";
    String ROUTE_PROTOCOL = "route";