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 int getPriority() {
        return DEFAULT_PRIORITY;
    }
    @Override
    public boolean isRuntime() {
        return tagRouterRule != null && tagRouterRule.isRuntime();
    }
    @Override
    public boolean isForce() {
        
        return tagRouterRule != null && tagRouterRule.isForce();
    }
    private boolean isForceUse(Invocation invocation) {
        return Boolean.valueOf(invocation.getAttachment(FORCE_USE_TAG, url.getParameter(FORCE_USE_TAG, "false")));
    }
    private <T> List<Invoker<T>> filterInvoker(List<Invoker<T>> invokers, Predicate<Invoker<T>> predicate) {
        return invokers.stream()
                .filter(predicate)
                .collect(Collectors.toList());
    }
    private boolean addressMatches(URL url, List<String> addresses) {
        return addresses != null && addresses.contains(url.getAddress());
    }
    private boolean addressNotMatches(URL url, List<String> addresses) {
        return addresses == null || !addresses.contains(url.getAddress());
    }
    public void setApplication(String app) {
        this.application = app;
    }