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 URL getUrl() {
        return url;
    }
    @Override
    public <T> List<Invoker<T>> route(List<Invoker<T>> invokers, URL url, Invocation invocation) throws RpcException {
        if (CollectionUtils.isEmpty(invokers)) {
            return invokers;
        }
        if (tagRouterRule == null || !tagRouterRule.isValid() || !tagRouterRule.isEnabled()) {
            return invokers;
        }
        List<Invoker<T>> result = invokers;
        String tag = StringUtils.isEmpty(invocation.getAttachment(TAG_KEY)) ? url.getParameter(TAG_KEY) :
                invocation.getAttachment(TAG_KEY);
        
        if (StringUtils.isNotEmpty(tag)) {
            List<String> addresses = tagRouterRule.getTagnameToAddresses().get(tag);
            
            if (CollectionUtils.isNotEmpty(addresses)) {
                result = filterInvoker(invokers, invoker -> addressMatches(invoker.getUrl(), addresses));
                
                if (CollectionUtils.isNotEmpty(result) || tagRouterRule.isForce()) {
                    return result;
                }
            } else {
                
                
                result = filterInvoker(invokers, invoker -> tag.equals(invoker.getUrl().getParameter(TAG_KEY)));
            }