显然这与Facebook的循环DNS结构有关。我猜想Facebook的地址之一失败，并且服务器仍然尝试连接到该地址，因为DNS缓存。

Apparently this is related with the round-robin DNS structure of Facebook. I guess one of the addresses of the Facebook failed and the server was still trying to connect to that address because of the DNS cache.

主机提供商必须清除其DNS缓存才能解决问题。

The hosting provider had to clear their DNS caches to resolve the problem.

有关轮次的更多信息-robin DNS，您可以访问 http://en.wikipedia.org/wiki/Round-robin_DNS 。

For more information about the round-robin DNS, you may visit http://en.wikipedia.org/wiki/Round-robin_DNS.