迭代 DNS 查找

Question

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（权威答案）位，如果它没有设置为 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 位仍然为 0，当我继续发送请求时，它似乎无处可去。这是进行迭代查找的正确方法吗？如果是这样，如何区分权威和非权威答案？这是向 1.1.1.1 服务器请求 google.com:

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)

Answer 1

Here's the result when asking 1.1.1.1 server for google.com:

DNS 查询并不总是以权威答案结尾。实际上，1.1.1.1是一个迭代解析器，所以查询相关服务器（root ->.com -> google.com）和return是他的工作最终答案不会是权威的，因为 1.1.1.1 是 return 的答案。然后它将缓存响应并 return 每当有人问他同样的问题时。

如果你想创建一个类似挖掘的工具并寻找 www.whosebug.com，你需要做 1.1.1.1 做的事情 - 从根开始（例如 a.root-servers.net.），并且询问 .com。然后询问 .com 服务器（例如 a.gtld-servers.net）关于 whosebug.com。最后，向负责whosebug.com（例如ns-1033.awsdns-01.org）的服务器询问www.whosebug.com的A/AAAA记录。你得到的答案应该是权威的：

> dig www.whosebug.com @ns-1033.awsdns-01.org                                                                                                                          ──(Thu,Apr08)─┘

; <<>> DiG 9.16.1-Ubuntu <<>> www.whosebug.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.whosebug.com.         IN      A

;; ANSWER SECTION:
www.whosebug.com.  3600    IN      CNAME   whosebug.com.
whosebug.com.      3600    IN      A       151.101.65.69
whosebug.com.      3600    IN      A       151.101.1.69
whosebug.com.      3600    IN      A       151.101.193.69
whosebug.com.      3600    IN      A       151.101.129.69

;; AUTHORITY SECTION:
whosebug.com.      172800  IN      NS      ns-1033.awsdns-01.org.
whosebug.com.      172800  IN      NS      ns-358.awsdns-44.com.
whosebug.com.      172800  IN      NS      ns-cloud-e1.googledomains.com.
whosebug.com.      172800  IN      NS      ns-cloud-e2.googledomains.com.

注意 aa 标志：flags: qr aa rd

迭代 DNS 查找

Iterative DNS lookup

python

dns

network-protocols