问题描述
我正在尝试使用 python 将 dig 的简单版本实现为一个项目。我想通过迭代实现 DNS 查找。我阅读了 RFC 文档,我想我应该检查响应中的 AA(Authoritative Answer) 位,如果它未设置为 1,我应该向给定响应中提供的 IP 发送相同的请求,直到该位为放。 当我尝试 google.com 并使用 wireshark 检查响应时,它提供了正确的 IP,但 AA 位仍为 0,当我不断发送请求时,它似乎无处可去。 这是进行迭代查找的正确方法吗?如果是,如何区分权威答案和非权威答案? 这是向 google.com 询问 1.1.1.1 服务器时的结果:
Flags: 0x8080 Standard query response,No error
1... .... .... .... = Response: Message is a response
.000 0... .... .... = Opcode: Standard query (0)
.... .0.. .... .... = Authoritative: Server is not an authority for domain
.... ..0. .... .... = Truncated: Message is not truncated
.... ...0 .... .... = Recursion desired: Don't do query recursively
.... .... 1... .... = Recursion available: Server can do recursive queries
.... .... .0.. .... = Z: reserved (0)
.... .... ..0. .... = Answer authenticated: Answer/authority portion was not authenticated by the server
.... .... ...0 .... = Non-authenticated data: Unacceptable
.... .... .... 0000 = Reply code: No error (0)
解决方法
这是向 1.1.1.1 服务器询问 google.com 时的结果:
DNS 查询并不总是以权威答案结束。实际上,1.1.1.1
是一个迭代解析器,因此他的工作是查询相关服务器 (root
->.com
-> google.com
) 并返回最终结果'不具有权威性,因为 1.1.1.1
是返回它的那个。然后它会缓存响应并在有人问他同样的问题时返回它。
如果你想创建一个类似 dig 的工具并寻找 www.stackoverflow.com
,你需要做 1.1.1.1
所做的 - 从一个根(例如 a.root-servers.net.
)开始,并询问它关于.com
。然后向 .com
服务器(例如 a.gtld-servers.net
)询问 stackoverflow.com
。最后,向负责 google.com
(例如 ns-1033.awsdns-01.org
)的服务器询问 A
/AAAA
的 www.stackoverflow.com
记录。你从中得到的答案应该是权威的:
> dig www.stackoverflow.com @ns-1033.awsdns-01.org ──(Thu,Apr08)─┘
; <<>> DiG 9.16.1-Ubuntu <<>> www.stackoverflow.com @ns-1033.awsdns-01.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY,status: NOERROR,id: 62794
;; flags: qr aa rd; QUERY: 1,ANSWER: 5,AUTHORITY: 4,ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0,flags:; udp: 4096
;; QUESTION SECTION:
;www.stackoverflow.com. IN A
;; ANSWER SECTION:
www.stackoverflow.com. 3600 IN CNAME stackoverflow.com.
stackoverflow.com. 3600 IN A 151.101.65.69
stackoverflow.com. 3600 IN A 151.101.1.69
stackoverflow.com. 3600 IN A 151.101.193.69
stackoverflow.com. 3600 IN A 151.101.129.69
;; AUTHORITY SECTION:
stackoverflow.com. 172800 IN NS ns-1033.awsdns-01.org.
stackoverflow.com. 172800 IN NS ns-358.awsdns-44.com.
stackoverflow.com. 172800 IN NS ns-cloud-e1.googledomains.com.
stackoverflow.com. 172800 IN NS ns-cloud-e2.googledomains.com.
注意 aa
标志:flags: qr aa rd