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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
public String getServices() {
        return services;
    }
    /**
     * It's an alias method for {@link #getServices()}, but the more convenient.
     *
     * @return the String {@link List} presenting the Dubbo interface subscribed
     * @since 2.7.8
     */
    @Deprecated
    @Parameter(excluded = true)
    public Set<String> getSubscribedServices() {
        return splitToSet(getServices(), COMMA_SEPARATOR_CHAR);
    }
    /**
     * Set the service names that the Dubbo interface subscribed.
     *
     * @param services If it is a multiple-values, the content will be a comma-delimited String.
     * @since 2.7.8
     */
    public void setServices(String services) {
        this.services = services;
    }
    @Override
    public T get() {
        if (destroyed) {
            throw new IllegalStateException("The invoker of ReferenceConfig(" + url + ") has already destroyed!");
        }
        if (ref == null) {
            //