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.
public static final String NAME = "TAG_ROUTER";
    private static final int DEFAULT_PRIORITY = 100;
    private static final Logger logger = LoggerFactory.getLogger(TagRouter.class);
    private static final String RULE_SUFFIX = ".tag-router";
    private TagRouterRule tagRouterRule;
    private String application;
    public TagRouter(DynamicConfiguration configuration, URL url) {
        super(configuration, url);
    }
    @Override
    public synchronized void process(ConfigChangeEvent event) {
        if (logger.isDebugEnabled()) {
            logger.debug("Notification of tag rule, change type is: " + event.getChangeType() + ", raw rule is:\n " +
                    event.getValue());
        }
        try {
            if (event.getChangeType().equals(ConfigChangeType.DELETED)) {
                this.tagRouterRule = null;
            } else {
                this.tagRouterRule = TagRuleParser.parse(event.getValue());
            }
        } catch (Exception e) {
            logger.error("Failed to parse the raw tag router rule and it will not take effect, please check if the " +
                    "rule matches with the template, the raw rule is:\n ", e);
        }
    }