使用dig/nslookup命令查看dns解析的方法步骤
dig-DNSlookuputility
当域名出现访问故障时,可以通过检查域名解析来判断是否是由错误的解析导致的问题。
1.域名解析无结果(不存在或被HOLD(未实名认证等))
2.域名解析到错误的IP(被阻断,被劫持响应错误结果,需要对解析流程做判断)
3.对应CNAME记录的值无法解析
4.部分解析异常(配置多个域名服务器时,多个服务器解析结果不一致,需要确认是否在DNS服务器上配置添加的解析记录一致)
简单使用解析一下www.baidu.com结果如下:
dig命令做迭代查询
在命令后加上+trace可以跟踪整个解析流程:
1.由根域名服务器查找到负责解析.com的顶级域名服务器
2.由顶级域名服务器查找到baidu.com的二级域名服务器
3.由二级域名服务器查找到www.baidu.com对应一条CNAME记录www.a.shifen.com
4.再去查找www.a.shifen.com对应的A记录
5.最后返回A记录对应的IP地址
[root@jia3~]#digwww.baidu.com+trace ;<<>>DiG9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6<<>>www.baidu.com+trace ;;globaloptions:+cmd .320307INNSa.root-servers.net. .320307INNSk.root-servers.net. .320307INNSi.root-servers.net. .320307INNSl.root-servers.net. .320307INNSb.root-servers.net. .320307INNSe.root-servers.net. .320307INNSh.root-servers.net. .320307INNSd.root-servers.net. .320307INNSg.root-servers.net. .320307INNSj.root-servers.net. .320307INNSf.root-servers.net. .320307INNSm.root-servers.net. .320307INNSc.root-servers.net. ;;Received228bytesfrom202.106.0.20#53(202.106.0.20)in98ms com.172800INNSc.gtld-servers.net. com.172800INNSl.gtld-servers.net. com.172800INNSd.gtld-servers.net. com.172800INNSh.gtld-servers.net. com.172800INNSm.gtld-servers.net. com.172800INNSa.gtld-servers.net. com.172800INNSk.gtld-servers.net. com.172800INNSb.gtld-servers.net. com.172800INNSe.gtld-servers.net. com.172800INNSg.gtld-servers.net. com.172800INNSj.gtld-servers.net. com.172800INNSi.gtld-servers.net. com.172800INNSf.gtld-servers.net. ;;Received491bytesfrom192.5.5.241#53(192.5.5.241)in93ms baidu.com.172800INNSdns.baidu.com. baidu.com.172800INNSns2.baidu.com. baidu.com.172800INNSns3.baidu.com. baidu.com.172800INNSns4.baidu.com. baidu.com.172800INNSns7.baidu.com. ;;Received201bytesfrom192.48.79.30#53(192.48.79.30)in501ms www.baidu.com.1200INCNAMEwww.a.shifen.com. a.shifen.com.1200INNSns1.a.shifen.com. a.shifen.com.1200INNSns2.a.shifen.com. a.shifen.com.1200INNSns5.a.shifen.com. a.shifen.com.1200INNSns3.a.shifen.com. a.shifen.com.1200INNSns4.a.shifen.com. ;;Received228bytesfrom220.181.37.10#53(220.181.37.10)in8ms
域名不存在时,dig命令如何返回
比如解析www.not-exists-domain.com这个域名,是不存在的。
整个过程如下:
1.由根域名返回.com顶级域的服务器地址
2.由.com顶级域查到二级域名不存在,返回一条SOA记录
[root@jia3~]#digwww.not-exists-domain.com+trace ;<<>>DiG9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6<<>>www.not-exists-domain.com+trace ;;globaloptions:+cmd .319714INNSb.root-servers.net. .319714INNSe.root-servers.net. .319714INNSh.root-servers.net. .319714INNSd.root-servers.net. .319714INNSg.root-servers.net. .319714INNSj.root-servers.net. .319714INNSf.root-servers.net. .319714INNSm.root-servers.net. .319714INNSc.root-servers.net. .319714INNSa.root-servers.net. .319714INNSk.root-servers.net. .319714INNSi.root-servers.net. .319714INNSl.root-servers.net. ;;Received228bytesfrom202.106.0.20#53(202.106.0.20)in105ms com.172800INNSe.gtld-servers.net. com.172800INNSc.gtld-servers.net. com.172800INNSj.gtld-servers.net. com.172800INNSl.gtld-servers.net. com.172800INNSk.gtld-servers.net. com.172800INNSg.gtld-servers.net. com.172800INNSm.gtld-servers.net. com.172800INNSa.gtld-servers.net. com.172800INNSi.gtld-servers.net. com.172800INNSh.gtld-servers.net. com.172800INNSb.gtld-servers.net. com.172800INNSf.gtld-servers.net. com.172800INNSd.gtld-servers.net. ;;Received503bytesfrom192.112.36.4#53(192.112.36.4)in228ms com.900INSOAa.gtld-servers.net.nstld.verisign-grs.com.1524576381180090060480086400 ;;Received116bytesfrom192.12.94.30#53(192.12.94.30)in333ms
nslookup-queryInternetnameserversinteractively
nslookup有交互式和非交互式两种使用方式如下图:
nslookup还可以指定到某个域名服务器做解析命令格式如下:
nslookupwww.baidu.com8.8.8.8(域名服务器地址)
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