關於dns非常奇怪的問題，請高手解答！
本單位dns伺服器，系統redhat9+bind9.2.1(系統默認安裝)，測試期間一直正常，最近正式使用卻發現問題，就是解析正常，偶爾會出現某些域名不能解析的情況！！
> www.taobao.com
Server:
Address: 172.18.212.254
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
*** Request to timed-out
在伺服器上dig結果如下：
; <<>> DiG 9.2.1 <<>> www.taobao.com +trace
;; global options: printcmd
. 494189 IN NS K.ROOT-SERVERS.NET.
. 494189 IN NS L.ROOT-SERVERS.NET.
. 494189 IN NS M.ROOT-SERVERS.NET.
. 494189 IN NS A.ROOT-SERVERS.NET.
. 494189 IN NS B.ROOT-SERVERS.NET.
. 494189 IN NS C.ROOT-SERVERS.NET.
. 494189 IN NS D.ROOT-SERVERS.NET.
. 494189 IN NS E.ROOT-SERVERS.NET.
. 494189 IN NS F.ROOT-SERVERS.NET.
. 494189 IN NS G.ROOT-SERVERS.NET.
. 494189 IN NS H.ROOT-SERVERS.NET.
. 494189 IN NS I.ROOT-SERVERS.NET.
. 494189 IN NS J.ROOT-SERVERS.NET.
;; Received 308 bytes from 172.18.212.254#53(172.18.212.254) in 2 ms
com. 172800 IN NS a.gtld-servers.net.
com. 172800 IN NS g.gtld-servers.net.
com. 172800 IN NS h.gtld-servers.net.
com. 172800 IN NS c.gtld-servers.net.
com. 172800 IN NS i.gtld-servers.net.
com. 172800 IN NS b.gtld-servers.net.
com. 172800 IN NS d.gtld-servers.net.
com. 172800 IN NS l.gtld-servers.net.
com. 172800 IN NS f.gtld-servers.net.
com. 172800 IN NS j.gtld-servers.net.
com. 172800 IN NS k.gtld-servers.net.
com. 172800 IN NS e.gtld-servers.net.
com. 172800 IN NS m.gtld-servers.net.
;; Received 492 bytes from 193.0.14.129#53(K.ROOT-SERVERS.NET) in 765 ms
taobao.com. 172800 IN NS ns1.taobao.com.
taobao.com. 172800 IN NS ns2.taobao.com.
;; Received 100 bytes from 192.42.93.30#53(g.gtld-servers.net) in 418 ms
dig: Couldn't find server 'ns1.taobao.com': Name or service not known
不知道各位遇到過這樣的情況沒有，小弟很著急，望高手出手相救！！
《解決方案》
只是這一個域名嗎？還是所有的？
