在tag route下， dubbo2.6作为client调用dubbo2.7 server，路由规则已经起效果； dubbo2.7作为client调用dubbo2.6路由规则没有生效。（在dubbo2.7，ops没有配置路由规则的前提下，只通过应用url的tag打标）。
发现问题代码, org.apache.dubbo.rpc.cluster.router.tag.TagRouter：
```
if (CollectionUtils.isEmpty(invokers)) {
            return invokers;
        }

        if (tagRouterRule == null || !tagRouterRule.isValid() || !tagRouterRule.isEnabled()) {
            return invokers;
        }
```
没在ops里配置路由规则的时候，需要继续往下走。

----transplate here 

Under tag route, dubbo2.6 calls dubbo2.7 server as client, routing rules have been effective; dubbo2.7 as client calls dubbo2.6 routing rules have not taken effect. (In dubbo2.7, ops is not configured with routing rules, only by applying the url tag).
Found the problem code, org.apache.dubbo.rpc.cluster.router.tag.TagRouter:
```
if (CollectionUtils.isEmpty(invokers)) {
            return invokers;
        }

        if (tagRouterRule == null || !tagRouterRule.isValid() || !tagRouterRule.isEnabled()) {
            return invokers;
        }
```
When you do not configure routing rules in ops, you need to continue down.
@Override
    public <T> void notify(List<Invoker<T>> invokers) {
        if (invokers == null || invokers.isEmpty()) {
            return;
        }
        Invoker<T> invoker = invokers.get(0);
        URL url = invoker.getUrl();
        String providerApplication = url.getParameter(Constants.REMOTE_APPLICATION_KEY);
        if (StringUtils.isEmpty(providerApplication)) {
            logger.error("TagRouter must getConfig from or subscribe to a specific application, but the application " +
                    "in this TagRouter is not specified.");
            return;
        }
        synchronized (this) {
            if (!providerApplication.equals(application)) {
                if (!StringUtils.isEmpty(application)) {
                    configuration.removeListener(application + RULE_SUFFIX, this);
                }
                String key = providerApplication + RULE_SUFFIX;
                configuration.addListener(key, this);
                application = providerApplication;
                String rawRule = configuration.getConfig(key);
                if (rawRule != null) {
                    this.process(new ConfigChangeEvent(key, rawRule));
                }
            }
        }
    }
}