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下面第一次查询递归解析说明a.gtld-servers.net 能解析出dns.baidu.com的ip地址
但是第二次查询迭代解析发现
a.gtld-servers.net
dig: couldn't get address for 'dns.baidu.com': not found
这是什么情况。
debian1:~# dig @a.gtld-servers.net www.baidu.com
; <<>> DiG 9.5.1-P1 <<>> @a.gtld-servers.net www.baidu.com
; (2 servers found)
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5247
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 4, ADDITIONAL: 4
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;www.baidu.com. IN A
;; AUTHORITY SECTION:
baidu.com. 172800 IN NS dns.baidu.com.
baidu.com. 172800 IN NS ns2.baidu.com.
baidu.com. 172800 IN NS ns3.baidu.com.
baidu.com. 172800 IN NS ns4.baidu.com.
;; ADDITIONAL SECTION:
dns.baidu.com. 172800 IN A 202.108.22.220
ns2.baidu.com. 172800 IN A 61.135.165.235
ns3.baidu.com. 172800 IN A 220.181.37.10
ns4.baidu.com. 172800 IN A 220.181.38.10
;; Query time: 506 msec
;; SERVER: 192.5.6.30#53(192.5.6.30)
;; WHEN: Fri Nov 13 17:38:52 2009
;; MSG SIZE rcvd: 167
debian1:~# dig @a.gtld-servers.net www.baidu.com +trace
; <<>> DiG 9.5.1-P1 <<>> @a.gtld-servers.net www.baidu.com +trace
; (2 servers found)
;; global options: printcmd
. 172800 IN NS k.root-servers.net.
. 172800 IN NS e.root-servers.net.
. 172800 IN NS f.root-servers.net.
. 172800 IN NS b.root-servers.net.
. 172800 IN NS a.root-servers.net.
. 172800 IN NS i.root-servers.net.
. 172800 IN NS j.root-servers.net.
. 172800 IN NS d.root-servers.net.
. 172800 IN NS h.root-servers.net.
. 172800 IN NS c.root-servers.net.
. 172800 IN NS g.root-servers.net.
. 172800 IN NS l.root-servers.net.
. 172800 IN NS m.root-servers.net.
;; Received 512 bytes from 192.5.6.30#53(192.5.6.30) in 515 ms
com. 172800 IN NS B.GTLD-SERVERS.NET.
com. 172800 IN NS C.GTLD-SERVERS.NET.
com. 172800 IN NS D.GTLD-SERVERS.NET.
com. 172800 IN NS E.GTLD-SERVERS.NET.
com. 172800 IN NS F.GTLD-SERVERS.NET.
com. 172800 IN NS G.GTLD-SERVERS.NET.
com. 172800 IN NS H.GTLD-SERVERS.NET.
com. 172800 IN NS I.GTLD-SERVERS.NET.
com. 172800 IN NS J.GTLD-SERVERS.NET.
com. 172800 IN NS K.GTLD-SERVERS.NET.
com. 172800 IN NS L.GTLD-SERVERS.NET.
com. 172800 IN NS M.GTLD-SERVERS.NET.
com. 172800 IN NS A.GTLD-SERVERS.NET.
;; Received 491 bytes from 192.228.79.201#53(b.root-servers.net) in 5994 ms
baidu.com. 172800 IN NS dns.baidu.com.
baidu.com. 172800 IN NS ns2.baidu.com.
baidu.com. 172800 IN NS ns3.baidu.com.
baidu.com. 172800 IN NS ns4.baidu.com.
;; Received 167 bytes from 192.5.6.30#53(A.GTLD-SERVERS.NET) in 518 ms
dig: couldn't get address for 'dns.baidu.com': not found |
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