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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
package org.apache.dubbo.config;
import org.apache.dubbo.common.utils.StringUtils;
import org.apache.dubbo.config.support.Parameter;
import org.apache.dubbo.rpc.model.ModuleModel;
import org.apache.dubbo.rpc.support.ProtocolUtils;
import static org.apache.dubbo.common.constants.CommonConstants.INVOKER_LISTENER_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.REFERENCE_FILTER_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.REFER_ASYNC_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.ROUTER_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.STUB_EVENT_KEY;
import static org.apache.dubbo.common.constants.RegistryConstants.PROVIDED_BY;
import static org.apache.dubbo.common.constants.RegistryConstants.PROVIDER_PORT;
/**
 * AbstractConsumerConfig
 *
 * @export
 * @see ReferenceConfigBase
 */
public abstract class AbstractReferenceConfig extends AbstractInterfaceConfig {
    private static final long serialVersionUID = -2786526984373031126L;
    
    /**
     * Check if service provider exists, if not exists, it will be fast fail
     */
    protected Boolean check;
    /**
     * Whether to eagle-init
     */
    protected Boolean init;
    /**