我正在尝试使用 NSLOOKUP 来了解递归 DNS 查找。我正在查找一个虚假的主机名，无论我启用还是禁用递归，我似乎都会得到相同的结果。
使用递归：
nslookup
Default Server: UnKnown
Address: ::1
> set recurse
> set debug
> nytimes
Server: UnKnown
Address: ::1
------------
Got answer:
HEADER:
opcode = QUERY, id = 2, rcode = NXDOMAIN
header flags: response, auth. answer, want recursion, recursion avail.
questions = 1, answers = 0, authority records = 1, additional = 0
QUESTIONS:
nytimes.intranet.contoso.com, type = A, class = IN
AUTHORITY RECORDS:
-> intranet.contoso.com
ttl = 3600 (1 hour)
primary name server = DNSSERVER.intranet.contoso.com
responsible mail addr = hostmaster.intranet.contoso.com
serial = 10301
refresh = 900 (15 mins)
retry = 600 (10 mins)
expire = 86400 (1 day)
default TTL = 3600 (1 hour)
------------
------------
Got answer:
HEADER:
opcode = QUERY, id = 3, rcode = NXDOMAIN
header flags: response, auth. answer, want recursion, recursion avail.
questions = 1, answers = 0, authority records = 1, additional = 0
QUESTIONS:
nytimes.intranet.contoso.com, type = AAAA, class = IN
AUTHORITY RECORDS:
-> intranet.contoso.com
ttl = 3600 (1 hour)
primary name server = DNSSERVER.intranet.contoso.com
responsible mail addr = hostmaster.intranet.contoso.com
serial = 10301
refresh = 900 (15 mins)
retry = 600 (10 mins)
expire = 86400 (1 day)
default TTL = 3600 (1 hour)
------------
------------
Got answer:
HEADER:
opcode = QUERY, id = 4, rcode = NOERROR
header flags: response, want recursion, recursion avail.
questions = 1, answers = 1, authority records = 0, additional = 0
QUESTIONS:
nytimes.contoso.com, type = A, class = IN
ANSWERS:
-> nytimes.contoso.com
internet address = 74.125.226.195
ttl = 1800 (30 mins)
------------
Non-authoritative answer:
------------
Got answer:
HEADER:
opcode = QUERY, id = 5, rcode = NOERROR
header flags: response, want recursion, recursion avail.
questions = 1, answers = 0, authority records = 1, additional = 0
QUESTIONS:
nytimes.contoso.com, type = AAAA, class = IN
AUTHORITY RECORDS:
-> contoso.com
ttl = 900 (15 mins)
primary name server = dns01.gpn.register.com
responsible mail addr = partnersupport.register.com
serial = 2002050701
refresh = 10800 (3 hours)
retry = 3600 (1 hour)
expire = 604800 (7 days)
default TTL = 3600 (1 hour)
------------
Name: nytimes.contoso.com
Address: 74.125.226.195
>
没有递归：
nslookup
Default Server: UnKnown
Address: ::1
> set norecurse
> set debug
> nytimes
Server: UnKnown
Address: ::1
------------
Got answer:
HEADER:
opcode = QUERY, id = 2, rcode = NXDOMAIN
header flags: response, auth. answer, recursion avail.
questions = 1, answers = 0, authority records = 1, additional = 0
QUESTIONS:
nytimes.intranet.contoso.com, type = A, class = IN
AUTHORITY RECORDS:
-> intranet.contoso.com
ttl = 3600 (1 hour)
primary name server = DNSSERVER.intranet.contoso.com
responsible mail addr = hostmaster.intranet.contoso.com
serial = 10301
refresh = 900 (15 mins)
retry = 600 (10 mins)
expire = 86400 (1 day)
default TTL = 3600 (1 hour)
------------
------------
Got answer:
HEADER:
opcode = QUERY, id = 3, rcode = NXDOMAIN
header flags: response, auth. answer, recursion avail.
questions = 1, answers = 0, authority records = 1, additional = 0
QUESTIONS:
nytimes.intranet.contoso.com, type = AAAA, class = IN
AUTHORITY RECORDS:
-> intranet.contoso.com
ttl = 3600 (1 hour)
primary name server = DNSSERVER.intranet.contoso.com
responsible mail addr = hostmaster.intranet.contoso.com
serial = 10301
refresh = 900 (15 mins)
retry = 600 (10 mins)
expire = 86400 (1 day)
default TTL = 3600 (1 hour)
------------
------------
Got answer:
HEADER:
opcode = QUERY, id = 4, rcode = NOERROR
header flags: response, recursion avail.
questions = 1, answers = 1, authority records = 0, additional = 0
QUESTIONS:
nytimes.contoso.com, type = A, class = IN
ANSWERS:
-> nytimes.contoso.com
internet address = 74.125.226.195
ttl = 1526 (25 mins 26 secs)
------------
Non-authoritative answer:
------------
Got answer:
HEADER:
opcode = QUERY, id = 5, rcode = NOERROR
header flags: response, recursion avail.
questions = 1, answers = 0, authority records = 1, additional = 0
QUESTIONS:
nytimes.contoso.com, type = AAAA, class = IN
AUTHORITY RECORDS:
-> contoso.com
ttl = 626 (10 mins 26 secs)
primary name server = dns01.gpn.register.com
responsible mail addr = partnersupport.register.com
serial = 2002050701
refresh = 10800 (3 hours)
retry = 3600 (1 hour)
expire = 604800 (7 days)
default TTL = 3600 (1 hour)
------------
Name: nytimes.contoso.com
Address: 74.125.226.195
>
即使我将其设置为关闭，它似乎也在使用递归。有趣的是，如果我查找指定 4.2.2.2 作为 DNS 服务器的虚假主机名，则递归设置确实会生效。有人知道为什么会发生这种情况吗？
顺便说一下，我清理了主机名
答案1
当您设置后，服务器会返回该域的权威响应norecurse，并且愿意为您执行递归。无论是否设置了递归标志都无关紧要。
得到答案：HEADER：标头标志： 回复，授权答案，递归有用。