squid 偶尔会Server Failure 求助！

kko1983

我用iptables+squid实现了代理服务器上网，平时上网都很正常，但有时候打开网页时会出现：
While trying to retrieve the URL: http://news.sina.com.cn/
The following error was encountered:
Unable to determine IP address from host name for news.sina.com.cn
The dnsserver returned:
Server Failure: The name server was unable to process this query.
This means that:
The cache was not able to resolve the hostname presented in the URL.
Check if the address is correct.
Your cache administrator is root.
不是所有的网页都这样，只有部分网页会这样。当时的网络没有问题，客户机
上nslookup和ping都正常。我重启了squid后也不会出现这种问题，但是过段
时间后（这端时间长短不固定，好像没有规律）又会这样，求各位达人们指点一下，急!