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.
if (CollectionUtils.isNotEmpty(result) || isForceUse(invocation)) {
                return result;
            }
            
            else {
                List<Invoker<T>> tmp = filterInvoker(invokers, invoker -> addressNotMatches(invoker.getUrl(),
                        tagRouterRule.getAddresses()));
                return filterInvoker(tmp, invoker -> StringUtils.isEmpty(invoker.getUrl().getParameter(TAG_KEY)));
            }
        } else {
            
            
            List<String> addresses = tagRouterRule.getAddresses();
            if (CollectionUtils.isNotEmpty(addresses)) {
                result = filterInvoker(invokers, invoker -> addressNotMatches(invoker.getUrl(), addresses));
                
                if (CollectionUtils.isEmpty(result)) {
                    return result;
                }
                
                
            }
            return filterInvoker(result, invoker -> {
                String localTag = invoker.getUrl().getParameter(TAG_KEY);
                return StringUtils.isEmpty(localTag) || !tagRouterRule.getTagNames().contains(localTag);
            });
        }
    }