好久没写blog了，前段时间一直在忙着开发uchome手机版，今天来跟大家分享一个小技巧。
linux下有个很有用的工具dig，用它可以查看到某个域名的指向情况。例如，查看www.sina.com.cn的域名指向：
-bash-3.1$ dig http://www.sina.com.cn
; <<>> DiG 9.3.3rc2 <<>> http://www.sina.com.cn
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45409
;; flags: qr rd ra; QUERY: 1, ANSWER: 12, AUTHORITY: 3, ADDITIONAL: 3;; QUESTION SECTION:
;www.sina.com.cn. IN A;; ANSWER SECTION:
http://www.sina.com.cn. 57 IN CNAME jupiter.sina.com.cn.
jupiter.sina.com.cn. 599 IN CNAME newscd.sina.com.cn.
newscd.sina.com.cn. 42 IN A 221.236.31.150
newscd.sina.com.cn. 42 IN A 221.236.31.151
newscd.sina.com.cn. 42 IN A 221.236.31.152
newscd.sina.com.cn. 42 IN A 221.236.31.140
newscd.sina.com.cn. 42 IN A 221.236.31.141
newscd.sina.com.cn. 42 IN A 221.236.31.142
newscd.sina.com.cn. 42 IN A 221.236.31.143
newscd.sina.com.cn. 42 IN A 221.236.31.144
newscd.sina.com.cn. 42 IN A 221.236.31.145
newscd.sina.com.cn. 42 IN A 221.236.31.149;; AUTHORITY SECTION:
sina.com.cn. 11027 IN NS ns3.sina.com.cn.
sina.com.cn. 11027 IN NS ns1.sina.com.cn.
sina.com.cn. 11027 IN NS ns2.sina.com.cn.;; ADDITIONAL SECTION:
ns2.sina.com.cn. 31983 IN A 61.172.201.254
ns3.sina.com.cn. 22464 IN A 202.108.44.55
ns1.sina.com.cn. 39791 IN A 202.106.184.166;; Query time: 35 msec
;; SERVER: 61.139.2.69#53(61.139.2.69)
;; WHEN: Fri Nov 27 22:23:44 2009
;; MSG SIZE rcvd: 338
在这里可以看到www.sina.com.cn这个域名的指向情况。www.sina.com.cn的CNAME指向jupiter.sina.com.cn，而jupiter.sina.com.cn的CNAME又指向newscd.sina.com.cn，最后newscd.sina.com.cn的A记录指向了多个IP地址（多台服务器），这样做用来实现DNS负载均衡。