<!-- If you need to report a security issue please visit https://github.com/apache/dubbo/security/policy -->

- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.

## Ask your question here
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
if (logger.isInfoEnabled()) {
                logger.info("The url already exists, mesh no longer processes url: " + url);
            }
            return;
        }
        // 
        String podNamespace;
        if (StringUtils.isEmpty(System.getenv("POD_NAMESPACE"))) {
            if (logger.isWarnEnabled()) {
                logger.warn(CONFIG_FAILED_LOAD_ENV_VARIABLE, "", "", "Can not get env variable: POD_NAMESPACE, it may not be running in the K8S environment , " +
                    "finally use 'default' replace.");
            }
            podNamespace = "default";
        } else {
            podNamespace = System.getenv("POD_NAMESPACE");
        }
        // 
        String providedBy = referenceParameters.get(PROVIDED_BY);
        // 
        String clusterDomain = Optional.ofNullable(System.getenv("CLUSTER_DOMAIN")).orElse(DEFAULT_CLUSTER_DOMAIN);
        // 
        Integer meshPort = Optional.ofNullable(getProviderPort()).orElse(DEFAULT_MESH_PORT);
        // 
        meshPort = meshPort > -1 ? meshPort : DEFAULT_MESH_PORT;
        // 
        url = TRIPLE + "://" + providedBy + "." + podNamespace + SVC + clusterDomain + ":" + meshPort;
    }
    /**
     * check if mesh config is correct
     *