1.开心网的主站采用了DNS轮询技术，所谓DNS轮询，就是一个域名对应几条A记录，如开心网的主站有6台服务器
DNS轮询有一个缺点，如果域名所指向的某一个台服务器或几台服务器出现了问题（如Web服务器停止服务)，则DNS轮询无法判断
C:/Users/caihuafeng>nslookup www.kaixin001.com
服务器: ns.crcbj.com
Address: 61.233.9.9
非权威应答:
名称: a.kaixin001.com
Addresses: 220.181.100.30
220.181.100.35
220.181.100.33
220.181.100.34
220.181.100.32
220.181.100.31
Aliases: www.kaixin001.com
2.a.kaixin001.com应该是域名www.kaixin001.com的别名，也就是大家用http://a.kaixin001.com/同样可以访问开心网
C:/Users/caihuafeng>nslookup a.kaixin001.com
服务器: ns.crcbj.com
Address: 61.233.9.9
非权威应答:
名称: a.kaixin001.com
Addresses: 220.181.100.31
220.181.100.35
220.181.100.32
220.181.100.34
220.181.100.33
220.181.100.30
3.查询域名服务器ns.crcbj.com的一些情况
C:/Users/caihuafeng>nslookup -qt=ns ns.crcbj.com
服务器: ns.crcbj.com
Address: 61.233.9.9
crcbj.com
primary name server = dns7.hichina.com
responsible mail addr = hostmaster.hichina.com
serial = 2008070200
refresh = 3600 (1 hour)
retry = 600 (10 mins)
expire = 604800 (7 days)
default TTL = 3600 (1 hour)
4.查看开心网的邮件服务器情况
根据nslookup查询出的情况，我猜想mail1.kaixin001.com及mail2.kaixin002.com应该是开心网的邮件服务器，开心网有上千万的用户，专门有两台邮件服务器是比较正常的;另外ns1.kaixin001.com ~ ns4.kaixin001.com这4台服务器应该是开心网的域名服务器
C:/Users/caihuafeng>nslookup -qt=mx kaixin001.com
服务器: ns.crcbj.com
Address: 61.233.9.9
非权威应答:
kaixin001.com MX preference = 10, mail exchanger = mail1.kaixin001.com
kaixin001.com MX preference = 20, mail exchanger = mail2.kaixin001.com
kaixin001.com nameserver = ns3.kaixin001.com
kaixin001.com nameserver = ns1.kaixin001.com
kaixin001.com nameserver = ns2.kaixin001.com
kaixin001.com nameserver = ns4.kaixin001.com
mail2.kaixin001.com internet address = 123.125.59.127
mail1.kaixin001.com internet address = 119.161.132.228
ns2.kaixin001.com internet address = 220.181.100.173
ns1.kaixin001.com internet address = 123.103.102.240
ns3.kaixin001.com internet address = 119.161.132.240
ns4.kaixin001.com internet address = 123.125.57.13
5.开心网域名解析过程的模拟
在默认情况下nslookup使用的是我们在本机TCP/IP配置中的DNS服务器进行查询，但有时候我们需要指定一个特定的服务器进行查询试验。这时候我们不需要更改本机的TCP/IP配置，只要在命令后面加上指定的服务器IP或者域名就可以了。这个参数在我们对一台指定服务器排错是非常必要的，另外我们可以通过指定服务器直接查询授权服务器的结果避免其他服务器缓存的结果
例如下面的测试在域名服务器f.gtld-servers.net下找不到域名www.kaixin001.com解析结果，而在域名服务器ns1.kaixin001.com下能查询到域名www.kaixin001.com解析结果，说明域名服务器ns.kaixin001.com保持有域名www.kaixin001.com的信息
C:/Users/caihuafeng>nslookup -norecurse www.kaixin001.com f.gtld-servers.net
(root) nameserver = c.root-servers.net
(root) nameserver = h.root-servers.net
(root) nameserver = b.root-servers.net
(root) nameserver = f.root-servers.net
(root) nameserver = d.root-servers.net
(root) nameserver = a.root-servers.net
(root) nameserver = j.root-servers.net
(root) nameserver = l.root-servers.net
(root) nameserver = g.root-servers.net
(root) nameserver = e.root-servers.net
(root) nameserver = k.root-servers.net
(root) nameserver = i.root-servers.net
(root) nameserver = m.root-servers.net
c.root-servers.net internet address = 192.33.4.12
h.root-servers.net internet address = 128.63.2.53
h.root-servers.net AAAA IPv6 address = 2001:500:1::803f:235
b.root-servers.net internet address = 192.228.79.201
f.root-servers.net internet address = 192.5.5.241
f.root-servers.net AAAA IPv6 address = 2001:500:2f::f
d.root-servers.net internet address = 128.8.10.90
a.root-servers.net internet address = 198.41.0.4
a.root-servers.net AAAA IPv6 address = 2001:503:ba3e::2:30
j.root-servers.net internet address = 192.58.128.30
j.root-servers.net AAAA IPv6 address = 2001:503:c27::2:30
l.root-servers.net internet address = 199.7.83.42
g.root-servers.net internet address = 192.112.36.4
服务器: UnKnown
Address: 192.35.51.30
*** UnKnown 找不到 www.kaixin001.com: BAD ERROR VALUE
C:/Users/caihuafeng>nslookup -norecurse www.kaixin001.com ns1.kaixin001.com
DNS request timed out.
timeout was 2 seconds.
服务器: UnKnown
Address: 123.103.102.240
名称: a.kaixin001.com
Addresses: 220.181.100.31
220.181.100.30
220.181.100.34
220.181.100.32
220.181.100.33
220.181.100.35
Aliases: www.kaixin001.com
同理输入nslookup -norecurse www.kaixin001.com ns2.kaixin001.com,nslookup -norecurse www.kaixin001.com ns3.kaixin001.com,nslookup -norecurse www.kaixin001.com ns4.kaixin001.com也会有类似的解析结果，只不过Addresses后面的ip地址输出顺序不完全一样。