when run the nslookup command in the CMD windows,DNS server cannot display it‘s host name.
such as :
server:unkonwn
ip address:192.168.1.13
The real cause is that DNS server has never configurated the PTR record for it‘s host name.
so we need to add it into the reserved zone.
原文：http://www.cnblogs.com/yongdaiblog-201409/p/6798850.html