如果无法联系到整个区域的服务器,那么这个事实需要缓存多长时间？
解决方法
在BIND 9.11中,默认情况下,SERVFAIL响应缓存1秒.
从BIND管理员参考手册：
servfail-ttl
Sets the number of seconds to cache a
SERVFAILresponse due to DNSSEC validation failure or other general server failure. If set to 0,SERVFAILcaching is disabled. TheSERVFAILcache is not consulted if a query has theCD(Checking Disabled) bit set; this allows a query that Failed due to DNSSEC validation to be retried without waiting for theSERVFAILTTL to expire.The maximum value is 30 seconds; any higher value will be silently reduced. The default is 1 second.
这是根据RFC 2308实现的,尽管在实践中发现其中指定的最大超时是有问题的,因此当前默认为什么.
