linux - dig +trace解析结果为什么不显示上一层的域名？
使用dig追踪dns解析全过程的时候，
Received 169 bytes from 192.12.94.30#53(192.12.94.30)
为什么括号中不显示上一层的域名而是ip？
下面是网上别人博客的结果
$ dig +trace roclinux.cn
; <<>> DiG 9.2.4 <<>> +trace roclinux.cn
;; global options: printcmd
. 335937 IN NS l.root-servers.net.
. 335937 IN NS b.root-servers.net.
. 335937 IN NS d.root-servers.net.
. 335937 IN NS k.root-servers.net.
. 335937 IN NS h.root-servers.net.
. 335937 IN NS j.root-servers.net.
. 335937 IN NS a.root-servers.net.
. 335937 IN NS e.root-servers.net.
. 335937 IN NS c.root-servers.net.
. 335937 IN NS m.root-servers.net.
. 335937 IN NS g.root-servers.net.
. 335937 IN NS i.root-servers.net.
. 335937 IN NS f.root-servers.net.
;; Received 400 bytes from 10.23.0.231#53(10.23.0.231) in 0 ms //从本地DNS查找到根域DNS列表
cn. 172800 IN NS c.dns.cn.
cn. 172800 IN NS a.dns.cn.
cn. 172800 IN NS b.dns.cn.
cn. 172800 IN NS e.dns.cn.
cn. 172800 IN NS ns.cernet.net.
cn. 172800 IN NS d.dns.cn.
;; Received 292 bytes from 192.228.79.201#53(b.root-servers.net) in 460 ms //选择了b.root-servers.net这台根域DNS来查找cn.域DNS列表
roclinux.cn. 21600 IN NS ns11.edong.com.
roclinux.cn. 21600 IN NS ns12.edong.com.
;; Received 76 bytes from 203.119.27.1#53(c.dns.cn) in 0 ms //选择了c.dns.cn这台cn.域DNS服务器来查找roclinux.cn的DNS列表
roclinux.cn. 3600 IN A 116.255.245.206
roclinux.cn. 3600 IN NS ns12.edong.com.
roclinux.cn. 3600 IN NS ns11.edong.com.
;; Received 124 bytes from 61.147.124.145#53(ns11.edong.com) in 104 ms //最终查找到A记录下面是我的结果
$ dig +trace roclinux.cn
; <<>> DiG 9.8.3-P1 <<>> +trace roclinux.cn
;; global options: +cmd
. 247860 IN NS g.root-servers.net.
. 247860 IN NS m.root-servers.net.
. 247860 IN NS e.root-servers.net.
. 247860 IN NS i.root-servers.net.
. 247860 IN NS a.root-servers.net.
. 247860 IN NS k.root-servers.net.
. 247860 IN NS f.root-servers.net.
. 247860 IN NS d.root-servers.net.
. 247860 IN NS h.root-servers.net.
. 247860 IN NS l.root-servers.net.
. 247860 IN NS b.root-servers.net.
. 247860 IN NS c.root-servers.net.
. 247860 IN NS j.root-servers.net.
;; Received 228 bytes from 10.3.9.4#53(10.3.9.4) in 30 ms
cn. 172800 IN NS d.dns.cn.
cn. 172800 IN NS ns.cernet.net.
cn. 172800 IN NS e.dns.cn.
cn. 172800 IN NS b.dns.cn.
cn. 172800 IN NS c.dns.cn.
cn. 172800 IN NS a.dns.cn.
;; Received 292 bytes from 2001:500:84::b#53(2001:500:84::b) in 301 ms
roclinux.cn. 86400 IN NS ns12.edong.com.
roclinux.cn. 86400 IN NS ns11.edong.com.
;; Received 76 bytes from 203.119.29.1#53(203.119.29.1) in 99 ms
roclinux.cn. 3600 IN A 116.255.245.206
roclinux.cn. 3600 IN NS ns11.edong.com.
roclinux.cn. 3600 IN NS ns12.edong.com.
;; Received 92 bytes from 58.215.76.153#53(58.215.76.153) in 31 ms我的结果中括号中的内容都是ip而不是域名，很不理解。
我的环境是 osX操作系统 教育网 有ipv6，希望大神帮忙解答。谢谢。
