DNS解释问题

各位大侠,请指教,我安装了一台DNS服务器,现在用NSLOOKU去查看时有点不对,出现DNS 超时
nslookup
Default server: server.mydomain.com
Address: 192.168.2.200
> set type=all
> mydomain.com
server:server.mydomain.com
address:192.168.2.200
DNS Request timed out
    timeout was 2 seconds.
mydomain.com       internet address=192.168.2.200
mydomain.com       nameserver=server.mydomain.com
.......
这是为什么,谢谢!